Power line communications method and apparatus

ABSTRACT

System, for transmitting and receiving signals over residential electrical cables includes at least one active wire, one neutral wire and one ground wire. The system includes at least two power line modems, each one of the two power line modems including a processor, transmitters and at least one receiver, transmitters and the receiver being coupled with the processor, for respectively transmitting and receiving the signals. At least two of the wires form at least one receive wire pair and at least two of the wires form at least one transmit wire pair. Each one of the transmitters defines a respective carrier wave range over the transmit wire pair, the processor determining a frequency carrier wave for the signals when the signals are transmitted. A given one of the transmitters transmits the signals if the frequency carrier wave is in the carrier wave range of the given one of the transmitters.

This application is a Continuation of International Application No.PCT/IL2010/000522 filed 29 Jun. 2010, which claims benefit of U.S. Ser.No. 61/221,125, filed 29 Jun. 2009 and U.S. Ser. No. 61/357,866, filed23 Jun. 2010 and which applications are incorporated herein byreference. To the extent appropriate, a claim of priority is made toeach of the above disclosed applications.

FIELD OF THE DISCLOSED TECHNIQUE

The disclosed technique relates to power line communication, in general,and to methods and systems for enabling power line communication signalsto be switched between power line pairs, in particular.

BACKGROUND OF THE DISCLOSED TECHNIQUE

Power line communication (herein abbreviated PLC) refers to methods andsystems for enabling data to be transferred over electrical cables. PLCis also referred to in the art as power line digital subscriber line,power line carrier, mains communication, power line telecom and powerline networking. In the case that PLC is used to provide access to theInternet, or for video distribution over a network, the methods andsystems are referred to as broadband over power lines (hereinabbreviated BPL). Electrical cables can also be referred to as powercables, power lines, electrical power lines, electrical wiring,electrical cabling and the like. These terms are used interchangeablyherein and represent the cabling used to transfer electricity from anelectricity provider, such as an electric company (e.g. Pacific Gas &Electric, Florida Power & Light, etc. . . .) or an electricity generator(e.g., a wind energy converter), to a residence, as well as the wiresused in a residence to transfer electricity to various wall sockets,electrical outlets, wall plugs and power points in the residence. PLCenables various devices, such as computers, printers, televisions andother electrical devices in a residence, to be coupled with one another,as a network, without the need for new wires to be added to theresidence. A residence can refer to a private home, an apartmentbuilding, an office building or other structures where people live thatreceive electricity. Each device to be coupled in the network requires aseparate element for enabling it to transfer data over the electricalwiring. Such an element is usually referred to as a modem, and commonlyreferred to in the art as a power line modem. Such modems usuallytransfer data in the high frequency range, which is usually on the orderof megahertz or higher. PLC methods are known in the art.

US Patent Application Publication No. 2008/0057866 A1, issued toSchwager et al., entitled “Method for transmitting a signal on a powerline network, transmitting unit, receiving unit and system” is directedto a system and method for transmitting a signal on a PLC network. ThePLC system includes first and second diversity PLC-modems connected to apower line network, e.g. a building network. The PLC-modems use thepower-line network to transmit and receive data. The power-line networkincludes three lines: phase (P), neutral (N) and protective earth (PE).The PLC-modems are connected to and utilize all three lines bytransmitting data on pairs of the lines: P-N, N-PE or P-PE. Thereceiving PLC-modem includes a transmitting unit T and a receiving unitR, which is adapted to receive DM (i.e., differential mode) signals fromany combination of lines. The transmission unit T includes a signalgenerator, a transmitter and a transmitter connector. The receiver unitR includes a receiver connector, a receiver and a combiner. The signalgenerator of the transmitting unit T is coupled to the transmitter. Thetransmitter connector connects the transmitter to all of the threenetwork lines (P, N, PE). The receiver connector of the receiving unit Rconnects the receiver to all of the three network lines. The receiver iscoupled to the combiner. A receiving connector may be adapted to act asa transmitting connector and vice-versa when transmitting or receivingsignals in the other direction. The signal generator of the transmittingunit T receives a signal from which at least two auxiliary signals aregenerated. The auxiliary signals are transmitted through at least twotransmission channels. The receiver of the receiving unit R receives thetwo auxiliary signals. The two received auxiliary signals aretransmitted to the combiner, which combines the signals in order toobtain the original signal. A transmission channel may use two out ofthe three pairs of lines for signal feeding and all three combinationsof pairs for receiving. Measurements show that different transmissionchannels obtain different fading characteristics for different frequencybands. Channel characteristics are evaluated by the transmitting unit Tand receiving unit R of the intended transmitting and receivingPLC-modems prior to or during the transmission of the at least twoauxiliary signals. According to the aforementioned evaluation, thetransmission unit T determines which feeding channels are best suitedfor the specific transmission frequency band, which is intended to beused or in use. Evaluation of channel characteristics should be measuredover time, since it may change in time. Advanced diversity techniquesmay be used, such as MIMO (i.e., Multiple-In Multiple-Out), therebyallowing transmission of different signals over the individualtransmission links. If so, channel evaluation is performed for eachindividual link. Transmission channels may differ in, but are notlimited to, the frequency domain, phase domain, time domain or spatialdomain. Common mode signals may be detected in addition.

US Patent Application Publication No. 2009/0060060 A1, issued toStadelmeier et al., entitled “Method for transmitting a signal from atransmitter to a receiver in a power line communication network,transmitter, receiver, power line communication modem and power linecommunication system” is directed to a system and method fortransmitting signals in PLC networks. The PLC system includes first andsecond PLC modems in a MIMO mode. Each PLC modem may be used as bothtransmitter and receiver, thereby forming a bidirectional communicationnetwork. The PLC modems are connected to a home installation. The homeinstallation includes three wires: phase line (P), neutral line (N) andprotective earth (PE). Feeding signals are performed between a pair ofthe wires, hence allowing three possible transmission paths: P-N, N-PEand P-PE. The PLC modem, which is in a transmission mode, uses twotransmission paths, and the PLC modem, which is in a receiving mode,uses all three possible transmission paths. In addition, a common mode(CM) path may be used. The transmitting PLC modem transmits an initialdata burst, which includes a training sequence, to the receiving PLCmodem. The receiving PLC modem evaluates the MIMO channels andcalculates encoding and decoding matrices from the evaluated MIMOchannels' eigenvalues and an adaptive OFDM tonemap. A feedback data istransmitted back to the transmitting PLC modem. The receiving PLC modemselects the adaptive OFDM tonemap for decoding and a correspondingdecoding eigenbeamforming matrix. The transmitting PLC modem selects theadaptive OFDM and the encoding eigenbeamforming matrix according to thefeedback data in order to build a message. The message is transmitted tothe receiving PLC modem, which uses the adaptive OFDM tonemap and thedecoding eigenbeamforming matrix in order to generate the originalmessage.

US Patent Application Publication No. 2008/0273613 A1, issued to Kol,entitled “Multiple input, multiple output (MIMO) communication systemover in-premises wires” is directed to a multiple channel power linecommunication system. The system includes a plurality of MIMO devices.The MIMO devices are PLC devices, which utilize the in-premises powerline network in order to transfer data. The in-premises power-linenetwork includes a phase line (P), a neutral line (N) and a ground line(G). Each MIMO device may include a transmitter and a receiver. Thetransmitter may include a MIMO transmit processor and multiple analogfront-ends (AFEs). The reciever may include a MIMO receive processor andmultiple analog front-ends (AFEs). Each AFE included within thetransmitter or the receiver may include a digital to analog converter(DAC), an analog to digital converter (ADC) and an analog and/or digitalfilters, mixers and amplifiers. Each AFE is connected to a pair of linesselected out of the phase, neutral and ground lines (i.e., P-N, N-G orP-G), where each such combination of lines forms a channel ofcommunication. The transmit processor processes an input data stream tobe transmitted. The transmit processor may generate two independentsignals from a signal which is designated for transmission. The transmitprocessor then may transmit each independent signal by a different AFE,thereby by a different channel. AFEs within the receiver may receive theindependent signals and process them. The received signals may include acontribution from the “straight path” (the channel through which theyare connected) and the “cross path” (the channels through which theyaren't connected). The receive processor utilizes information concerningthe frequency-response of the different channels in order to reconstructthe two independent transmitted signals and to produce an output datastream. The channels may be also used to increase channel diversity bytransmitting the same information through multiple channels. In thiscase, the transmit processor may include a space-time encoder and thereceive processor may include a space-time decoder. The transceiver andreceiver may each include a mode negotiator. The mode negotiator mayselect, with respect to each channel, between two modes: transmittingtwo independent signals (multiplexing) or transmitting the same signalthrough multiple channels (spatial diversity). The selection is madebased on the measured channel characteristics and requested speed. Inanother embodiment, a single transceiver may communicate in abidirectional manner with two different transceivers through twodifferent channels, each channel including a combination of a pair oflines (P-N, N-G or P-G). Thus, two independent data streams may flowthrough two different channels simultaneously and use overlappingfrequency bands.

An article entitled “MIMO for Inhome Power Line Communications,” to L.Stadelmeier et al., is directed to MIMO schemes for inhome applications.In many parts of the world, the inhome installation includes three wires(Phase, Neutral and Ground) leading to three differential feedingpossibilities: P-N, N-G, P-G. Only two out of the three possiblecombinations may be used in the transmitting end and all three may beused in the receiving end. Capacity calculations are performed inprivate flats and houses. The capacity may be calculated as the sum oftwo independent SISO channels. There may be several MIMO arrangementswhich differ in the number of transmit and receive ports. Two basic MIMOschemes may be applied to an OFDM based PLC system. One is spatialmultiplexing, in which different signals are transmitted over differenttransmit ports and capacity gain is achieved. The other is space-time orspace-frequency encoding, in which a signal is transmitted throughmultiple transmit ports, thereby obtaining diversity gain and increasedcertainty in the signal received. Measurements show that the MIMOschemes show better performance than the existing SISO schemes and showincreases in channel capacity.

An article entitled “Space-Frequency Coded OFDM Systems for Multi-WirePower Line Communications,” to C. L. Giovaneli et al., published in theproceedings of the International Symposium on Power Line Communicationsand Its Applications, 2005, pages 191-195, is directed to aspace-frequency coded orthogonal frequency-division multiplexing (OFDM)system for high-speed data transmission over frequency selectivemulti-phase power line channels. In the absence of channel knowledge atthe transmitter end, frequency and space diversities are achieved bytransmitting the same data symbol over two uncoupled wires and over twodifferent carriers which are frequency-separated by carriers that aregreater than the coherence bandwidth of the channels. It is assumed thatchannel state information is available at the receiver end. DifferentMIMO-OFDM techniques are known for power line channels which includefour power line cables (three phase cables and neutral, e.g., accessdomain, large building or industrial plants). A basic multi-wiredifferential signaling structure used by the scheme proposed includes atransmitter and a receiver. The transmitter includes two elementaldifferential transmitters and a processor unit. The receiver includestwo elemental differential receivers, a space-frequency (SF) linearcombiner and a maximum-likelihood (ML) detector. Thus, the systemutilizes two pairs of cables and forms two independent orthogonal SISOchannels. The processor unit pre-codes the input data symbols prior totransmission and similarly pre-codes the orthogonal SISO-OFDM datasymbols. The OFDM data symbols are transmitted serially over the twoorthogonal SISO channels. The data symbols are received at eachreceiving point. The SF linear combiner realigns the output signals fromone channel and its associated estimation with respect to the signalsand estimation of the output signals of the other channel. After therealigning operation, the two signals include the same transmitted datasymbol. The combiner additionally performs linear combining by using themethod of maximal-ratio combining (MRC). The ML detector detects theoptimal data symbol at the output of the SF linear combiner. Simulationresults show that the proposed schemes perform significantly better thanthe conventional single-wire OFDM systems and that the symbol error rate(SER) of the proposed scheme outperforms the conventional SISO schemewhen the power line channel is corrupted by impulsive noise.

SUMMARY OF THE PRESENT DISCLOSED TECHNIQUE

It is an object of the disclosed technique to provide a novel method andsystem for power line modems in which the data transferred overelectrical wires in a residence can be transferred over various pairs ofwires in the residence, the wire pair chosen for transferring data beingselectable via a switch, which overcomes the disadvantages of the priorart.

In accordance with the disclosed technique, there is thus provided asystem for transmitting and receiving signals over residentialelectrical cables. The residential electrical cables include an activewire, a neutral wire and a ground wire. The system includes at least twopower line modems. Each one of the power line modems includes aprocessor, a plurality of transmitters and at least one receiver. Thetransmitters and the receiver are coupled with the processor. Thetransmitters are for transmitting the signals and the receiver is forreceiving the signals. At least two of the wires forms at least onereceive wire pair and at least two of the wires forms at least onetransmit wire pair. The processor is for determining a frequency carrierwave for the signals when the signals are transmitted. Each one of thetransmitters defines a respective carrier wave range over the transmitwire pair. A given one of the transmitters transmits the signals if thefrequency carrier wave of the signals is in the respective carrier waverange of the given one of the transmitters. Each one of the power linemodems couples a respective electrical device with a respectiveelectrical socket, each respective electrical socket being coupled withthe residential electrical cables.

According to another aspect of the disclosed technique, there is thusprovided a system for transmitting and receiving signals overresidential electrical cables. The residential electrical cables includean active wire, a neutral wire and a ground wire. The system includes atleast two power line modems. Each power line modem includes a processor,at least one transmitter, at least one receiver and at least one switch.The transmitter and the receiver are coupled with the processor. Theswitch is coupled with at least one of the transmitter and the receiver.The transmitter is for transmitting the signals and the receiver is forreceiving the signals. The switch is coupled with the active wire, theneutral wire and the ground wire. At least two of the wires form aplurality of wire pairs. The switch enables at least one of thetransmitter and the receiver to be coupled with at least one of a firstwire pair and a second wire pair respectively. Each one of the powerline modems couples a respective electrical device with a respectiveelectrical socket, each respective electrical socket being coupled withthe residential electrical cables.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosed technique will be understood and appreciated more fullyfrom the following detailed description taken in conjunction with thedrawings in which:

FIG. 1 is a schematic illustration of electrical sockets, constructedand operative in accordance with an embodiment of the disclosedtechnique;

FIG. 2 is a schematic illustration of 1-phase and 3-phase electricalwiring in a residence, constructed and operative in accordance withanother embodiment of the disclosed technique;

FIG. 3A is a schematic illustration of the communication channels in aMIMO PLC network, constructed and operative in accordance with a furtherembodiment of the disclosed technique;

FIG. 3B is a schematic illustration of a MIMO PLC network between twonodes, constructed and operative in accordance with another embodimentof the disclosed technique;

FIG. 4A is a schematic illustration of a first embodiment of a switchedPLC network between two nodes, constructed and operative in accordancewith a further embodiment of the disclosed technique;

FIG. 4B is a schematic illustration of a second embodiment of a switchedPLC network between two nodes, constructed and operative in accordancewith another embodiment of the disclosed technique;

FIG. 4C is a schematic illustration of a third embodiment of a switchedPLC network between two nodes, constructed and operative in accordancewith a further embodiment of the disclosed technique;

FIG. 4D is a schematic illustration of an MRC PLC network between twonodes, constructed and operative in accordance with another embodimentof the disclosed technique;

FIG. 4E is a schematic illustration of a switched MRC PLC networkbetween two nodes, constructed and operative in accordance with afurther embodiment of the disclosed technique;

FIG. 4F is a schematic illustration of a switched MRC PLC per carriernetwork between two nodes, constructed and operative in accordance withanother embodiment of the disclosed technique;

FIG. 5 is a schematic illustration of a modem of the prior art;

FIG. 6A is a schematic illustration of a receiver section of a switchedPLC modem, constructed and operative in accordance with a furtherembodiment of the disclosed technique;

FIG. 6B is a schematic illustration of another receiver section of aswitched PLC modem, constructed and operative in accordance with anotherembodiment of the disclosed technique;

FIG. 6C is a schematic illustration of a further receiver section of aswitched PLC modem, constructed and operative in accordance with afurther embodiment of the disclosed technique;

FIG. 6D is a schematic illustration of a transmitter section of aswitched PLC modem, constructed and operative in accordance with anotherembodiment of the disclosed technique;

FIG. 6E is a schematic illustration of another transmitter section of aswitched PLC modem, constructed and operative in accordance with afurther embodiment of the disclosed technique;

FIG. 6F is a schematic illustration of a further transmitter section ofa switched PLC modem, constructed and operative in accordance withanother embodiment of the disclosed technique;

FIG. 7A is a schematic illustration of a first communication channelcoordination scheme in a switched PLC network between two nodes,constructed and operative in accordance with a further embodiment of thedisclosed technique;

FIG. 7B is a schematic illustration of a second communication channelcoordination scheme in a switched PLC network between two nodes,constructed and operative in accordance with another embodiment of thedisclosed technique;

FIG. 7C is a schematic illustration of a third communication channelcoordination scheme in a switched PLC network between two nodes,constructed and operative in accordance with a further embodiment of thedisclosed technique;

FIG. 7D is a schematic illustration of a fourth communication channelcoordination scheme in a switched PLC network between two nodes,constructed and operative in accordance with another embodiment of thedisclosed technique; and

FIG. 7E is a schematic illustration of a communication channelcoordination method in a switched PLC network between a plurality ofnodes, constructed and operative in accordance with a further embodimentof the disclosed technique.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The disclosed technique overcomes the disadvantages of the prior art byproviding a novel power line modem configuration and PLC method forenabling the data transferred over electrical wires in a residence to betransferred over various pairs of wires in the residence. The wire pairchosen for transferring data is selected via a switch. By enabling thechoice of which wire pair to transfer data on, transmission speeds aresubstantially improved over the prior art. In addition, data transferrates are significantly improved in PLC systems with a minimal increasein manufacturing costs for producing PLC modems according to thedisclosed technique

Reference is now made to FIG. 1, is a schematic illustration ofelectrical sockets, generally referenced 100, constructed and operativein accordance with an embodiment of the disclosed technique. FIG. 1shows two different types of electrical sockets, an electrical socket102 and an electrical socket 104. Electrical socket 102 represents aType B electrical socket as found in residences in North America andJapan. Electrical socket 104 represents a Type H electrical socket asfound in residences in Israel. Electrical sockets 102 and 104 representthe shape and form of wall sockets to which electrical devices can beplugged into as well as the shape and form of electrical plugs which canbe plugged into these sockets. As can be seen, each of electricalsockets 102 and 104 respectively includes three contacts. Electricalsocket 102 includes a live contact 106, a neutral contact 108 and aground contact 110. Electrical socket 104 includes a live contact 112, aneutral contact 114 and a ground contact 116. In general, electricitywhich is transferred to residences is transferred over electricalcabling in the residence which contains three wires. A first wire isknown as the active, live, phase, line or hot wire (herein these termsare used interchangeably) and is usually symbolized on electrical plugsand sockets using the tilde symbol ‘˜’. A second wire is known as theneutral, cold or return wire (herein these terms are usedinterchangeably) and is usually symbolized on electrical plugs andsockets using the capital letter ‘N’. A third wire is known as theground, earth, safety ground or safety earth wire (herein these termsare used interchangeably) and is usually symbolized on electrical plugsand sockets using the capital letter ‘G’ or an arrow pointing downwardsas shown in FIG. 1 adjacent to ground contacts 110 and 116.

Each wire in the electrical cabling in a residence begins at an electricbox (not shown), which is coupled with an electricity provider. It isthrough the electric box that electricity, or electric current, isprovided to the residence from the electricity provider. From theelectric box, electrical cabling is used to provide electricity tovarious electrical sockets in the residence. Each electrical cablecoming out of the electric box eventually terminates at an electricalsocket, with each wire in the electrical cable terminating at one of thecontacts of the electrical socket. For example, regarding electricalsocket 102, the live wire (not shown) terminates at live contact 106,the neutral wire (not shown) terminates at neutral contact 108 and theground wire (not shown) terminates at ground contact 110. As shown inFIG. 1, each of the contacts is shaped or configured differently so thatthe wires in the electrical cable in a wall socket correspond to thewires in the electrical cable in a device plugged into the wall socket.In general, the live wire is used to transfer alternating current(herein abbreviated AC) electricity from the electric box to a load(i.e., an electrical device) plugged into a wall socket. The neutralwire is used to complete the electrical circuit back from the load tothe electric box. The neutral wire is also used to dissipate staticelectricity charges which may buildup in the load. The ground wire isused to transfer electricity when a load has an insulation flaw, usuallyback to the electric box. The transferred electricity is used to blow afuse or trip a circuit breaker in the electric box and substantiallystops the transfer of electricity to the electrical socket in which theload was plugged into. Such is the case when the current drawn from theelectrical socket by the load exceeds a predefined threshold. The groundwire is also used to dispose of unwanted electrical charges, as in thecase of surge protectors.

In PLC, devices are coupled to one another in a network via the wires inthe electrical cabling of a residence. In general, each device coupledto an electrical socket having a power line modem (i.e., it can transferdata over the electrical cabling of the residence) can be referred to asa node in a network. According to the disclosed technique, nodes canrepresent any electrical device in a residence which includes a powerline modem, such as computers, printers, televisions, DVD players, airconditioners, ovens, fridges and the like. To transfer data betweennodes, usually two wires (of the three wires present in an electricalcable), also known as a wire pair, are required. In general, since thedata is transferred as electromagnetic radiation over the electriccabling of a residence, other sources of electromagnetic radiation inthe vicinity may interfere with the data being transmitted. Thisinterference is known as radio frequency (herein abbreviated RF)ingress. To overcome this interference a wire pair (i.e., two wires) inthe electrical cabling is used as it is assumed that the RF ingress willradiate and interfere with the signals in all the wires in theelectrical cabling by substantially the same amount. To extract the datafrom the signal, the difference in the signal between a wire pair isdetermined. Since the RF ingress is common to both wires, it issubstantially eliminated in the difference calculation. In this respect,the transfer of data over a wire pair can be considered a differentialtransfer of data. By using a wire pair to transfer the data, thesusceptibility of the wires to RF ingress is mitigated. Such atransmission mode is called a differential transmission mode.

In a single electrical cable, three wire pairs are present, the ˜/N(live/neutral) wire pair, the N/G (neutral/ground) wire pair and the ˜/G(live/ground) wire pair. In state of the art power line modems, the ˜/Nwire pair is used to transfer data. In other words, in state of the artpower line modems, data is transferred to and from nodes via the liveand neutral wires in the electrical cabling in a residence. It is notedthat a wire pair can be considered like a communication channel.Therefore, state of the art power line modems use a single communicationchannel for transferring data over electrical cables.

Reference is now made to FIG. 2, which is a schematic illustration of1-phase and 3-phase electrical wiring in a residence, generallyreferenced 140, constructed and operative in accordance with anotherembodiment of the disclosed technique. In various countries, differentmethods are used by which electricity is distributed in a residence toits various electrical sockets. Shown in FIG. 2 are two of the mainmethods used to distribute electricity, commonly known as 1-phaseelectrical distribution and 3-phase electrical distribution. Forexample, all residential homes in France use 1-phase electricaldistribution, whereas homes in Germany use 3-phase electricaldistribution. In the USA, 2-phase electrical distribution, anothermethod, is used to provide electricity to high power devices. Electricalwiring 140 includes a 1-phase line power electric box 142 (hereinreferred to as electric box 142), electrical sockets 144, 146, 148, 150,152, 154 and 156, and electrical cables 158, 160, 162, 164, 166, 168 and170. Electrical cable 158 couples electrical socket 144 to electric box142, electrical cable 160 couples electrical socket 146 to electric box142, electrical cable 162 couples electrical socket 148 to electric box142, electrical cable 164 couples electrical socket 150 to electric box142, electrical cable 166 couples electrical socket 152 to electric box142, electrical cable 168 couples electrical socket 154 to electric box142 and electrical cable 170 couples electrical socket 156 to electricbox 142. Each of electrical cables 158, 160, 162, 164, 166, 168 and 170includes a live wire, a neutral wire and a ground wire. Electricalwiring 140 also includes a 3-phase line power electric box 172 (hereinreferred to as electric box 172), a first main fuse 174, a second mainfuse 176 and a third main fuse 178, a first set of electrical cables180, a second set of electrical cables 182 and a third set of electricalcables 184, and electrical sockets 186A, 186B, 186C, 186D, 188A, 188B,188C, 188D, 190A, 190B, 190C and 190D. First set of electrical cables180 couples electrical sockets 186A, 186B, 186C and 186D to first mainfuse 174, second set of electrical cables 182 couples electrical sockets188A, 188B, 188C and 188D to second main fuse 176 and third set ofelectrical cables 184 couples electrical sockets 190A, 190B, 190C and190D to third main fuse 178. It is noted that first set of electricalcables 180, second set of electrical cables 182 and third set ofelectrical cables 184 represent live wires going to each of electricalsockets 186A, 186B, 186C, 186D, 188A, 188B, 188C, 188D, 190A, 190B, 190Cand 190D. For purposes of clarity and simplicity, the neutral wire andground wire going to each electrical socket is not shown. In electricbox 172, the neutral wire and the ground wire going to each ofelectrical sockets 186A, 186B, 186C, 186D, 188A, 188B, 188C, 188D, 190A,190B, 190C and 190D originate from a single location (not shown) in theelectric box and not from separate main fuses as shown in FIG. 2regarding the live wire.

Electric box 142, as well as electric box 172, also known as the linepower or the mains power, represents the location in a residence (notshown) where transmission lines (not shown) used by an electricityprovider enter the residence. From electric box 142, electricity isprovided throughout the residence via electrical cabling, such aselectrical cables 158, 160, 162, 164, 166, 168 and 170, to variouselectrical sockets, such as electrical sockets 144, 146, 148, 150, 152,154 and 156. In general, the electrical sockets will be located invarious spaces and rooms in the residence, substantially covering theentire residence. Usually, every room in a residence has at least oneelectrical socket. In 1-phase electrical distribution, electricity issupplied to all electrical sockets in a residence at the same phase. Insuch a setup, an electrical device, i.e., a node, coupled to anyelectrical socket can communicate with another node coupled with anyother electrical socket using a power line modem. For example, acomputer (not shown), coupled with electrical socket 156, cancommunicate with a printer (not shown), coupled with electrical socket146, via electrical cables 170 and 160, respectively and electric box142. In 1-phase electrical distribution, since all electrical socketsare supplied with electricity at the same phase, i.e., substantially atthe same time, the maximum load, or the maximum amount of electricitythat can be used at any given time in the residence, is determined bygovernment regulations of how much electricity, as measured in amperes,is provided to different types of residences. In some countries, thegovernment regulation may be high enough that all the devices in aresidence, especially devices that use a lot of electricity, such as airconditioners and ovens, can run simultaneously. In other countries,however, the government regulation may not be high enough that all thedevices in a residence can run simultaneously, which may lead tosituations where an air conditioner and a dishwasher, or an oven, maynot be able to be run simultaneously in the residence, because the totalamount of electricity required to run those devices is higher than thepermitted amount of electricity which the residence can use in a giventime period. Such a situation can be remedied using 3-phase electricaldistribution.

In 3-phase electrical distribution, the electrical sockets are dividedup into three groups. Electrical sockets in each group are supplied withelectricity sequentially at different phases. For example, in electricbox 172, each phase is represented by a different main fuse. First mainfuse 174 represents a first phase, second main fuse 176 represents asecond phase and third main fuse 178 represents a third phase.Electrical sockets 186A, 186B, 186C and 186D are on the first phase,electrical sockets 188A, 188B, 188C and 188D are on the second phase andelectrical sockets 190A, 190B, 190C and 190D are on the third phase. Byplacing the electrical sockets of a residence on different phases,larger amounts of electricity can be used by devices in the residencewhile staying within the maximum amount of electricity being provided tothe residence. In this respect, 3-phase electrical distribution enablesmore devices to run in a residence than 1-phase electrical distribution.On the other hand, since the different electrical sockets coupled withelectric box 172 are on different phases, nodes on one phase cannotgenerally communicate with nodes on another phase, and if they can, itwill be at a substantially lower data transfer rate as signalattenuation between nodes on different phases is substantially higherthan signal attenuation between nodes on the same phase. As mentionedabove, in state of the art power line modem, the ˜/N wire pair is usedto transfer data. In 1-phase electrical distribution, since allelectrical sockets are on the same phase, nodes plugged into anyelectrical socket can communicate with one another at a substantiallyhigh data transfer rate. In 3-phase electrical distribution, since theelectrical sockets in a residence are on one of three different phases,only nodes plugged into electrical sockets wired in the same phase(i.e., wired to the same main fuse) can communicate with one another ata substantially high data transfer rate using state of the art powerline modems. For example, a computer (not shown) plugged into electricalsocket 186A cannot communicate with a printer (not shown) plugged intoelectrical socket 190C at a substantially high data transfer rate usingstate of the art power line modems, since the two electrical sockets areon different phases. It is noted though that only the electricitytransferred over the live wire is transferred sequentially at differentphases. Regarding the neutral wire and the ground wire, they are commonto all three phases. In other words, the neutral wire and ground wire toeach electrical socket in a residence originate from the same locationin electric box 172, whereas the live wires originate from one of firstmain fuse 174, second main fuse 176 or third main fuse 178. As describedbelow in much greater detail, with reference to FIGS. 3A, 3B, 4A, 4B,4C, 4D, 4E and 4F according to the disclosed technique, the wire pair inthe electrical cables used to transfer data can be selected. In the caseof 3-phase electrical distribution, if the N/G wire pair is selected,since this wire pair is common to all electrical sockets in theresidence, then even nodes on different phases can communicate with oneanother at a substantially high data transfer rate. For example, acomputer (not shown) plugged into electrical socket 186C couldcommunicate with a printer (not shown) plugged into electrical socket188D at a substantially high data transfer rate using a power line modemconstructed according to the disclosed technique, since a common wirepair between phases can be selected as the wire pair used to transferdata over the electrical cables of the residence. It is also noted thatin 3-phase electrical distribution, some of the electrical sockets (notshown) may be coupled with all three phases. Such is the case usuallyfor electrical sockets meant for high amperage devices, such as airconditioners and ovens.

Reference is now made to FIG. 3A, which is a schematic illustration ofthe communication channels in a multiple-input multiple-output (hereinabbreviated MIMO) PLC network, generally referenced 210, constructed andoperative in accordance with a further embodiment of the disclosedtechnique. In the art of analog and digital communication, the physicalmedium over which a signal can be transferred can be referred to as achannel. For example, in old telephone switchboard systems, each set ofwires over which telephone signals were transmitted representeddifferent channels. If all channels were in use, then no new telephonesignals could be sent by a new user (i.e., no new telephone calls couldbe made). In digital communication, the frequency, or frequency rangeused to transmit data (i.e., a signal) can also be referred to as achannel, such as the channels radio stations use to transmit radiobroadcasts. In order to transfer a signal over a channel, a transmitteris required to send, i.e. transmit, the signal over the channel. Thesignal is then received by a receiver coupled with the same channel,which accepts the signal. For example, a radio signal transmitted by atransmitter at 99.9 megahertz (herein abbreviated MHz) can be receivedby a radio tuned to 99.9 MHz, i.e., the receiver in the radio is set tothe specific channel, 99.9 MHz, used to transmit the radio signal. Inthe field of digital communication, devices which can transmit andreceive signals (i.e. data) over various types of cables, such as fiberoptic cables, telephone wires, Ethernet cables and electrical cables,are substantially referred to as modems. Modems may be designed totransmit data over a single channel or over a plurality of channels.State of the art modems usually have one transmitter and one receiver.

In the field of radio, cellular and wireless communication, varioustypes of communication configurations are known in the art. One suchconfiguration is known as a MIMO configuration, in which multipletransmitters transmit a signal over multiple channels and multiplereceivers are used to receive the signal transmitted over the multiplechannels. According to the disclosed technique, a MIMO configuration isused in a PLC network, as described below. In a PLC network, the variouswire pairs, ˜/N, N/G and ˜/G can be considered as differentcommunication terminals which can each access a direct communicationchannel and two crosstalk communication channels. Since electricalcables have three wires, two wire pairs, for example ˜/N and N/G, can beused to send two independent differential signals over the electricalcables. FIG. 3A includes a transmitter 212, a receiver 214, a ˜/Gtransmitting wire pair 216, a G/N transmitting wire pair 218, a ˜/Greceiving wire pair 220, a G/N receiving wire pair 222, a first directtransmission channel 224, a first crosstalk transmission channel 226, asecond crosstalk transmission channel 228 and a second directtransmission channel 230. It is noted that first direct transmissionchannel 224, first crosstalk transmission channel 226, second crosstalktransmission channel 228 and second direct transmission channel 230 donot represent the physical wiring coupling transmitter 212 and receiver214, but rather the communication channel model between transmitter 212and receiver 214. The direct transmission channels may coincide withparticular wire pairs, but the crosstalk communication channels do not.For purposes of simplicity, the term transmitter will herein beabbreviated TX and the term receiver will herein be abbreviated RX. TX212 and RX 214 are coupled via the transmission channels shown, meaningthe transmission channels shown represent the various channels throughwhich data can be transferred from TX 212 to RX 214. In general, TX 212is part of a modem (not shown) which is coupled with a node (which maybe a computer, printer, television and the like—also not shown). RX 214is also part of a modem (not shown), which is coupled with another nodein a network (not shown). For purposes of simplicity and to demonstratethe disclosed technique, only the TX of the node transmitting a signalis shown and only the RX of the node receiving the signal is shown inthis Figure as well as in FIGS. 3B, 4A, 4B, 4C, 4D, 4E and 4F. Asmentioned above, each node will have a modem coupled with it, the modemincluding a TX and an RX, meaning each node can communicate (i.e.,transmit and receive) with every other node. Also in general, a TX andan RX are each coupled to respective processors which can modify,code/decode and process data signals.

As FIG. 3A is a schematic illustration, each wire pair is shown as beingseparate. In a real electrical cable, only three wires are present andany two wire pairs will have a wire in common. According to thedisclosed technique, each wire pair can be considered a differentcommunication terminal by which the TX can transmit a signal. In a MIMOconfiguration, each TX transmits a signal to each RX. In FIG. 3A, eachwire pair can be considered a different communication terminal fortransmitting and receiving. Therefore, ˜/G transmitting wire pair 216can be considered a first transmission communication terminal, G/Ntransmitting wire pair 218 can be considered a second transmissioncommunication terminal, ˜/G receiving wire pair 220 can be considered afirst receiving communication terminal and G/N receiving wire pair 222can be considered a second receiving communication terminal. In the MIMOconfiguration of FIG. 3A, each transmitter transmits a signal to eachreceiver via one of four different transmission channels. ˜/Gtransmitting wire pair 216 transmits a signal using first directtransmission channel 224 to ˜/G receiving wire pair 220. G/Ntransmitting wire pair 218 transmits a signal using second directtransmission channel 230 to G/N receiving wire pair 222. ˜/Gtransmitting wire pair 216 also transmits a signal using first crosstalktransmission channel 226 to G/N receiving wire pair 222 and G/Ntransmitting wire pair 218 also transmits a signal using secondcrosstalk transmission channel 228 to ˜/G receiving wire pair 220. Adirect transmission channel is when both the receiving communicationterminal and the transmission communication terminal are on the samewire pair. In this respect, the wire pair represents a physical channel,as in the case shown in FIG. 3A of first direct transmission channel 224and second direct transmission channel 230. Since the data beingtransmitted over electrical cables is electromagnetic radiation and dueto the fact that in an electrical cable the three wires aresubstantially parallel and adjacent to one another, a second wire paircan pick up the signal being transferred over a first wire pair. This isrepresented in FIG. 3A as a crosstalk transmission channel. Crosstalktransmission channels exist in electrical cables, therefore even though˜/G transmitting wire pair 216 and G/N receiving wire pair 222 aredifferent wire pairs, the wire pairs can nonetheless transfer signalsfrom one to the other. It is noted that the choice of wire pairs shownin FIG. 3A (˜/G and G/N) is just illustrative and that any two of thethree possible wire pairs in an electrical cable can be used as thetransmitting wire pairs and the receiving wire pairs. In addition, thewire pairs in TX 212 and in RX 214 do not need to match up. All that isrequired for the configuration of FIG. 3A is that the TX transmit dataover two wire pairs and that two wire pairs receive the transmitteddata. For example, the two transmitting wire pairs in FIG. 3A could be a˜/G wire pair and an N/G wire pair (as shown in the figure) and the tworeceiving wire pairs could be a ˜/N wire pair and N/G wire pair.

It is noted that the communication channels shown in FIG. 3A are alwayspresent in a PLC communication network. In other words, the signaltransmitted over ˜/G transmitting wire pair 216 is received by both ˜/Greceiving wire pair 220 and G/N receiving wire pair 222. Likewise, thesame signal is transmitted over G/N transmitting wire pair 218 and isreceived by both ˜/G receiving wire pair 220 and G/N receiving wire pair222. The processor (not shown) coupled with RX 214 can separate the datawhich originated from each wire pair, as is known in the art. Below, inFIGS. 3B, 4A, 4B, 4C, 4D, 4E and 4F, different embodiments of thedisclosed technique are shown, and it is noted that in each of theseembodiments, the communication channels that are shown in FIG. 3A existin these embodiments as well because nodes (not shown) are coupled viaelectrical cables which have three wires and therefore three wire pairs.In other words, the physical coupling of a transmitter and a receiver ina PLC network using electrical cables enables the communication channelsin FIG. 3A between TX 212 and RX 214 to be present in each of theembodiments shown below, even though is some of these embodiments, thedata from a particular communication channel is discarded or notprocessed by a processor (not shown).

Reference is now made to FIG. 3B, which is a schematic illustration of aMIMO PLC network between two nodes, generally referenced 240,constructed and operative in accordance with another embodiment of thedisclosed technique. FIG. 3B can be viewed as an illustration of a MIMOPLC network system. MIMO PLC network 240 includes a TX 242 and an RX244. As mentioned in FIG. 3A, TX 242 is part of a modem (not shown)which is coupled with a node (not shown) and RX 244 is also part ofanother modem (not shown), which is also coupled with another node (notshown). Each modem may also include a processor (not shown). TX 242 andRX 244 are coupled via electrical cable 254. TX 242 receives a firstanalog signal 246 and a second analog signal 248. First analog signal246 is transmitted along electrical cable 254 via the ˜/N wire pair andsecond analog signal 248 is transmitted along electrical cable 254 viathe N/G wire pair. The wire pairs along which first analog signal 246and second analog signal 248 are transmitted to RX 244 are arbitrary andfor illustrative purposes only; any two of the three possible wire pairsin an electrical cable could have been used as the wire pairs fortransmitting the analog signals. RX 244 receives first analog signal 246and second analog signal 248 and outputs them as a first analog signal250 and a second analog signal 252. It is noted that first analog signal246 was transmitted over the direct communication channel of the ˜/Nwire pair but was also coupled via the crosstalk communication channelto second analog signal 252 received on the N/G wire pair. Likewise,second analog signal 248 was transmitted over the direct communicationchannel of the N/G wire pair but was also coupled via the crosstalkcommunication channel to first analog signal 250 received on the ˜/Nwire pair. In RX 244, first analog signal 250 represents the signal sentover the ˜/N wire pair as well as the signal sent over the N/G wire pairand second analog signal 252 represents the signal sent over the N/Gwire pair as well as the signal sent over the ˜/N wire pair. In theprocessor (not shown) coupled with RX 244, the original data which wasmodulated and used to generate the analog signals transmitted on eachwire pair is separated. As shown in FIG. 3A, in a MIMO configuration, asignal is transmitted over two wire pairs on the side of the transmitterand received by two wire pairs on the side of the receiver, i.e., thereare four communication channels between TX 242 and RX 244 as was shownin FIG. 3A. In addition, the two wire pairs on each of the transmitterside and the receiver side do not need to be the same.

In state of the art power line modems, only one wire pair is used totransmit data, which can result in a substantially low data transferrate of approximately 30 megabits per second (herein abbreviated Mbps)having a coverage of 90%. In general, the data transfer rates betweennodes in a network over electrical cables can have a wide range whichdepend on the distance between the nodes as well as the number and typeof electrical devices coupled with the various outlets in a residencewhere the network is located. Coverage refers to the percent of usersthat attain a given minimal data transfer rate after taking into accountthe factors which can affect data transfer rates and which are differentamongst users. In MIMO PLC network 240, since more than one wire pair isused to transmit and receive a signal, the data transfer rate can beincreased substantially. For example, if the signal transmitted over thecrosstalk communication channels is weak, then the two substantiallyindependent direct communication channels can be used to transmit twicethe amount of data, i.e., substantially twice the rate, over a singledirect communication channel, having a high signal to noise ratio(herein abbreviated SNR) while using the same amount of power totransmit the data. Data transfer rates are increased by sendingdifferent signals using different wire pairs simultaneously. Datatransfer rates are also increased by sending the same signal usingdifferent wire pairs simultaneously, thereby increasing the reliabilityand strength of the signal transferred. It is noted that the networkconfiguration in FIG. 3B is between two nodes. In the embodiment of thedisclosed technique shown in FIG. 3B, signals are transmitted from a TXto an RX in a PLC network using a MIMO configuration. In manyresidential configurations, errors in the signals received over aparticular wire pair may significantly affect the quality of the signaltransmitted, thereby not enabling the full increase in data transferrate in a MIMO configuration to be achieved. Nevertheless, increases inthe data transfer rate in a PLC network can be achieved via a switchedPLC network as described below in FIG. 4A.

Reference is now made to FIG. 4A, which is a schematic illustration of afirst embodiment of a switched PLC network between two nodes, generallyreferenced 280, constructed and operative in accordance with a furtherembodiment of the disclosed technique. Switched PLC network 280 includesa TX 282 and an RX 284. As mentioned in FIG. 3A, TX 282 is part of amodem (not shown) which is coupled with a node (not shown) and RX 284 isalso part of another modem (not shown), which is also coupled withanother node (not shown). A switch 296 is coupled with TX 282 and aswitch 298 is coupled with RX 284. Both switch 296 and switch 298 may berespectively coupled to respective processors (not shown). TX 282 iscoupled with RX 284 via electrical cable 294. The embodiment depicted inFIG. 4A is a double switched PLC network. TX 282 is wired to transmit ananalog signal either over a ˜/N wire pair or an N/G wire pair, dependingon the position of switch 296. In FIG. 4A, a first analog signal 286 isprovided to TX 282 which transmits it over the ˜/N wire pair. Firstanalog signal 286 is depicted as a solid line. If switch 296 wasswitched to its other position, then a second analog signal 288 would beprovided to TX 282 which would transmit it over the N/G wire pair.Second analog signal 288 is depicted by a dotted line. Likewise RX 284is wired to receive an analog signal either over a ˜/N wire pair or anN/G wire pair, depending on the position of switch 298. In FIG. 4A, asecond analog signal 292 is provided to RX 284 which received it overthe N/G wire pair. Second analog signal 292 is depicted as a solid line.If switch 298 was switched to its other position, then a first analogsignal 290 would be provided to RX 284 which would receive it over the˜/N wire pair. First analog signal 290 is depicted by a dotted line. Asexplained below, in FIG. 4A only one wire pair in each of TX 282 and RX284 has been selected to transmit and receive, respectfully, a signal.Due to the nature of the communication channels in a PLC network, whenTX 282 transmits first analog signal 286 over the ˜/N wire pair, thesignal is also transmitted over the crosstalk communication channel,which is why RX 284 can be set to receive the transmitted signal on theN/G wire pair as second analog signal 292. As mentioned above, thechoice of wire pairs to transmit and receive is arbitrary as any of thethree possible wire pairs can be used.

In general, electrical wires in a residence are noisy conductors. Thenoise results from many factors and can change over time. Some of thesefactors include the type of devices coupled to particular electricalsockets in the residence, the physical layout of the electrical wiringin a house, which is usually substantially branched in nature as well asRF ingress from devices in the vicinity (e.g., such as amateur radioequipment). In addition, signal attenuation on electrical wires may besubstantially large as electrical cabling is not usually manufactured tohandle the frequencies used in PLC (e.g., frequencies in the MHz rangeand higher) and protective elements for electrical devices plugged intothe residence, such as surge protectors, may increase signal loss athigh frequencies, such as those used in PLC. Due to these factors,different wire pairs may exhibit different transmission characteristics,such as different time-dependent noise characteristics. According to thedisclosed technique, a switch is provided on the transmission side of asignal and on the receiving side of the signal which enables the wirepair used to transmit the signal to be selected as well as the channelused by the receiver to receive the signal. Depending on these factors,at a given time interval, a particular wire pair may be less noisy thananother wire pair. In switched PLC network 280, switch 296 enables TX282 to transmit a signal over a first wire pair, such as the ˜/N wirepair or over a second wire pair, such as the N/G wire pair. Switch 298enables RX 284 to receive a signal over a first wire pair, such as the˜/N wire pair 290 or over a second wire pair, such as the N/G wire pair.Switch 296 enables different wire pairs to be selected to transmit ananalog signal whereas switch 298 enables different wire pairs to beselected to receive an analog signal. Depending on the wire pairselected in RX 284, either a direct communication channel or a crosstalkcommunication channel is selected for receiving signals. In the exampleshown in FIG. 4A, a ˜/N wire pair has been selected to transmit firstanalog signal 286, with an N/G wire pair selected to receive secondanalog signal 292. By selecting an N/G wire pair, which is a differentwire pair than the ˜/N wire pair, a crosstalk transmission channel hasbeen selected for transferring a signal from TX 282 to RX 284. Hadswitch 298 selected a ˜/N wire pair for receiving a signal from TX 282,a direct transmission channel would have been set up for transferring asignal from TX 282 to RX 284. As described below in FIGS. 6A-6F, a PLCmodem constructed according to the disclosed technique can check thenoise level and quality of each wire pair and determine, for a giventime interval, which wire pair on the side of the transmitter and whichwire pair on the side of the receiver should be used to achieve asubstantially high quality signal. It is noted that the networkconfiguration shown in FIG. 4A is between two nodes. According to thedisclosed technique, the choice of which wire pair on the side of thetransmitter and which wire pair on the side of the receiver is used totransmit and receive a signal is determined between two nodes. In anetwork with a plurality of nodes, each node has to negotiate with eachother node regarding which wire pair on the side of the transmitter andwhich wire pair on the side of the receiver is to be used between thetwo nodes.

As mentioned above, state of the art power line modems use the ˜/N wirepair for transferring signals between nodes. Also, as mentioned above,in 3-phase electrical distribution, the N/G wire pair is common to allthree phases, unlike the ˜ wire, which transfers electricity in threesequential phases. According to the embodiment in FIG. 4A, if two nodesin a 3-phase electrical distribution residence are located on differentphases, then the nodes can communicate at a substantially high datatransfer rate with one another by selecting to use the N/G wire pair onthe side of the TX of one node and on the side of the RX of the othernode for transferring signals. In addition, an increased number ofelectrical appliances coupled with electrical sockets of a particularphase (either 1-phase electrical distribution or 3-phase electricaldistribution) may increase the noise level on the ˜/N wire pair.According to the disclosed technique, the wire pair selected to transmitand receive signals can be changed depending on the noise level of eachwire pair. For example, if the noise level on the ˜/N is substantiallyhigh, because many electrical appliances are plugged in, then the N/Gwire pair can be selected for transferring signals. Even though thenoise from the ˜/N wire pair may still be received in the RX on the N/Gwire pair, the noise received would be from the crosstalk transmissionchannel, which is usually an attenuated signal, thereby resulting inless noise received with the signal. If the noise level of the ˜/Nreduces, because the electrical appliances are unplugged, then the TX ofone node and/or RX of the other node can switch back to using the ˜/Nwire pair to transfer signals if a higher quality signal can be sent onthat wire pair. Also, some surge protectors, for example those commonlyfound in the USA, are constructed such that in a power strip (also knownas a power bar), the surge protector is located between the ˜ wire andthe N wire of the power strip. Signals transmitted via the power stripat high frequencies (e.g., frequencies in the MHz range), commonly usedby power line modems, on the ˜/N wire pair experience a significantamount of signal attenuation because of the surge protectors.Significantly less attenuation is experienced by signals in such powerstrips on the N/G wire pair. Therefore, according to the disclosedtechnique, if a node is coupled with an electrical socket via a surgeprotector, the N/G wire pair can be used to transfer signals if theamount of attenuation of the ˜/N wire pair is substantially high.

As described below in greater detail in FIGS. 6A-6F, both TX 282 and RX284 are coupled with respective modems, which may include processors(not shown) and other electronics (not shown). These processors andother electronics are enabled to verify and check the varioustransmission channels available to determine which wire pair should beused to transfer data most efficiently. Methods and systems for checkingthe quality of a transmission channel are known in the art. According toan embodiment of the disclosed technique, the quality of eachtransmission channel is verified and checked at specific time intervals,which may be on the order of milliseconds, seconds, minutes or hours.Depending on the result of the check or verification, the wire pairsused to transfer signals between two nodes may be changed using switches296 and 298. In one embodiment of the disclosed technique, thetransmission side does the quality check of the wire pairs and channelsand instructs the receiving side which wire pair to use. In anotherembodiment of the disclosed technique, the receiving side does thequality check of the wire pairs and channels and instructs thetransmission side which wire pair to use. According to other embodimentsof the disclosed technique, as shown in below in FIGS. 4B and 4C,depending on various conditions, switch 296 may be disabled, switch 298may be disabled, or both switches may be disabled, such that either TX282, RX 284 or both work in a static manner, transmitting signals usinga particular wire pair and receiving signals over a particulartransmission channel. Such conditions can include financialconsiderations as well as the complexity of a PLC network and system.

Reference is now made to FIG. 4B, which is a schematic illustration of asecond embodiment of a switched PLC network between two nodes, generallyreferenced 310, constructed and operative in accordance with anotherembodiment of the disclosed technique. Switched PLC network 310 includesa TX 312 and an RX 314. As mentioned in FIG. 3A, TX 312 is part of amodem (not shown) which is coupled with a node (not shown) and RX 314 isalso part of another modem (not shown), which is also coupled withanother node (not shown). A switch 320 is coupled with TX 312. Switch320 may be coupled to a processor (not shown). TX 312 is coupled with RX314 via electrical cable 324. The embodiment depicted in FIG. 4B is asingle switched PLC network. TX 312 is wired to transmit an analogsignal either over a ˜/N wire pair or an N/G wire pair, depending on theposition of switch 320. In FIG. 4B, a first analog signal 316 isprovided to TX 312 which transmits it over the ˜/N wire pair. Firstanalog signal 316 is depicted as a solid line. If switch 320 wereswitched to its other position, then a second analog signal 318 would beprovided to TX 312 which would transmit it over the N/G wire pair.Second analog signal 318 is depicted by a dotted line. RX 314 is wiredto receive an analog signal only over an N/G wire pair. In FIG. 4B, ananalog signal 322 is provided to RX 314 which received it over the N/Gwire pair.

Switched PLC network 310 functions substantially like switched PLCnetwork 280 (FIG. 4A), except that only the transmission side isequipped with a switch. In FIG. 4B only one wire pair in TX 312 has beenselected to transmit a signal, whereas one wire pair in RX 314 has beendetermined (i.e., via the wiring) to receive a signal. Due to the natureof the communication channels in a PLC network, when TX 312 transmitsfirst analog signal 316 over the ˜/N wire pair, the signal is alsotransmitted over the crosstalk communication channel, which is why RX314 can receive the transmitted signal on the N/G wire pair as analogsignal 322. As mentioned above, the choice of wire pairs to transmit andreceive is arbitrary as any of the three possible wire pairs can beused. In other words, for example, RX 314 could have been wired to onlyreceive signals on the ˜/N wire pair or on the ˜/G wire pair. In thisembodiment, either the processor (not shown) coupled with TX 312 or theprocessor (not shown) coupled with RX 314 may check the quality of thetransmission channels to instruct switch 320 which wire pair should beused to transmit data. It is noted that in the embodiment shown in FIG.4B, the wire pair in TX 312 not used for transmitting signals maynonetheless transmit signals at predefined time intervals, according toinstructions received by the processor coupled with TX 312 or theprocessor coupled with RX 314. These transmitted signals can be used toperiodically monitor the transmission quality of the wire pair notcurrently being used by TX 312.

Reference is now made to FIG. 4C, which is a schematic illustration of athird embodiment of a switched PLC network between two nodes, generallyreferenced 340, constructed and operative in accordance with a furtherembodiment of the disclosed technique. Switched PLC network 340 includesa TX 342 and an RX 344. As mentioned in FIG. 3A, TX 342 is part of amodem (not shown) which is coupled with a node (not shown) and RX 344 isalso part of another modem (not shown), which is also coupled withanother node (not shown). A switch 352 is coupled with RX 344. Switch352 may be coupled to a processor (not shown). TX 342 is coupled with RX344 via electrical cable 354. The embodiment depicted in FIG. 4C is asingle switched PLC network. TX 342 is wired to transmit an analogsignal over a ˜/N wire pair. In FIG. 4C, an analog signal 346 isprovided to TX 342 which transmits it over the ˜/N wire pair. RX 344 iswired to receive either a first analog signal 348 over a ˜/N wire pairor a second analog signal 350 over an N/G wire pair, depending on theposition of switch 352. In the figure, RX 344 is switched to receivesecond analog signal 350 over the N/G wire pair. Second analog signal350 is depicted as a solid line. If switch 352 were switched to itsother position, then a first analog signal 348 would be provided to RX344 which would receive it over the ˜/N wire pair. First analog signal348 is depicted by a dotted line.

Switched PLC network 340 functions substantially like switched PLCnetwork 280 (FIG. 4A), except that only the receiving side is equippedwith a switch. In FIG. 4C only one wire pair in RX 342 has been selectedto receive a signal, whereas one wire pair in TX 342 has been determined(i.e., via the wiring) to transmit a signal. Due to the nature of thecommunication channels in a PLC network, when TX 342 transmits analogsignal 346 over the ˜/N wire pair, the signal is also transmitted overthe crosstalk communication channel, which is why RX 344 can receive thetransmitted signal on the N/G wire pair as second analog signal 350. Asmentioned above, the choice of wire pairs to transmit and receive isarbitrary as any of the three possible wire pairs can be used. In otherwords, for example, TX 342 could have been wired to only receive signalson the N/G wire pair or on the ˜/G wire pair. In this embodiment, eitherthe processor (not shown) coupled with TX 342 or the processor (notshown) coupled with RX 344 may check the quality of the transmissionchannels to instruct switch 352 which wire pair should be used toreceive data.

Reference is now made to FIG. 4D, which is a schematic illustration of amaximal ratio combining (herein abbreviated MRC) PLC network between twonodes, generally referenced 400, constructed and operative in accordancewith another embodiment of the disclosed technique. MRC PLC network 400includes a TX 402 and an RX 404. As mentioned in FIG. 4A, TX 402 is partof a modem (not shown) which is coupled with a node (not shown) and RX404 is also part of another modem (not shown), which is also coupledwith another node (not shown). TX 402 is coupled with RX 404 viaelectrical cable 412. TX 402 is wired to transmit an analog signal 406over an N/G wire pair. RX 404 receives a first analog signal 408 overthe ˜/N wire pair and a second analog signal 410 over the N/G wire pair.In FIG. 4D, only one wire pair is used by TX 402 to transmit a signal.It is noted that the wire pair which TX 402 is wired to in FIG. 4D isarbitrary and that any of the three possible wire pairs could have beenchosen. The same goes for the wire pairs used in RX 404 to receive thetransmitted signal.

FIG. 4D shows another embodiment of a PLC network. In this embodiment,TX 402 transmits one wire pair whereas RX 404 receives the signal overtwo wire pairs. The configuration shown in FIG. 4D uses a techniqueknown as MRC regarding the signals received in RX 404. Recall that RX404 receives a signal via the direct communication channel over the ˜/Nwire pair, as first analog signal 408 and another version of the samesignal again via the crosstalk communication channel over the N/G wirepair, as second analog signal 410. In MRC, two signals are received by areceiver, one on a direct transmission channel and another on acrosstalk transmission channel. In one embodiment of the MRC technique,depending on the quality of the signals received, the receiver decideswhich signal received from which channel is provided for furtherprocessing. In another embodiment of the MRC technique, the processor(not shown) coupled with the receiver, decides which signal received isprovided for further processing. In a further embodiment of the MRCtechnique, a weighted calculation is performed on the two signalsreceived on each wire pair to optimally combine them.

Reference is now made to FIG. 4E, which is a schematic illustration of aswitched MRC PLC network between two nodes, generally referenced 370,constructed and operative in accordance with a further embodiment of thedisclosed technique. Switched MRC PLC network 370 includes a TX 372 andan RX 374. As mentioned in FIG. 4A, TX 372 is part of a modem (notshown) which is coupled with a node (not shown) and RX 374 is also partof another modem (not shown), which is also coupled with another node(not shown). TX 372 is coupled with RX 374 via electrical cable 386. Aswitch 380 is coupled with TX 372. TX 372 can transmit a first analogsignal 376 over a ˜/N wire pair and a second analog signal 378 over anN/G wire pair, depending on the position of switch 380. RX 374 receivesa first analog signal 382 over the ˜/N wire pair and a second analogsignal 384 over the N/G wire pair. In FIG. 4E only one wire pair is usedby TX 372 to transmit a signal, therefore TX 372 transmits first analogsignal 376, shown as a solid line in the figure. If switch 380 were setto its other position, then TX 372 would transmit second analog 378,shown as a dotted line in the figure.

FIG. 4E shows another embodiment of the switched PLC network. In thisembodiment, TX 372 transmits over one selected wire pair at any giventime interval whereas RX 374 receives the signal over two wire pairs.The configuration shown in FIG. 4E uses a technique known as MRCregarding the signals received in RX 374. Recall that RX 374 receives asignal via the direct communication channel over the ˜/N wire pair, asfirst analog signal 382 and the same signal again via the crosstalkcommunication channel over the N/G wire pair, as second analog signal384. In MRC, two signals are received by a receiver, one on a directtransmission channel and another on a crosstalk transmission channel. Inone embodiment of the MRC technique, depending on the quality of thesignals received, the receiver decides which signal received from whichchannel is provided for further processing. In another embodiment of theMRC technique, the processor (not shown) coupled with the receiver,decides which signal received is provided for further processing. Forexample, in FIG. 4E, a processor (not show) coupled with RX 374 maycheck the signal received on the ˜/N wire pair and on the N/G wire pair.If the quality of the signal received on the N/G wire pair (i.e., thecrosstalk transmission channel) is higher than the quality of the signalreceived on the ˜/N wire pair (i.e., the direct transmission channel),then the processor may only process the signal received on the N/G wirepair and discard the signal received on the ˜/N wire pair. In a furtherembodiment of the MRC technique, a weighted calculation is performed onthe two signals received on each wire pair to optimally combine them.For example, in FIG. 4E, the signal received on the ˜/N wire pair may beoptimally combined with the signal received on the N/G wire pair in aprocessor (not shown), by combining a first portion of the signalreceived on the ˜/N wire pair with a second portion of the signalreceived on the N/G wire pair.

Reference is now made to FIG. 4F, which is a schematic illustration of aswitched MRC PLC per carrier network between two nodes, generallyreferenced 430, constructed and operative in accordance with anotherembodiment of the disclosed technique. Switched MRC PLC per carriernetwork 430 includes a transmitter section 432, which includes a firsttransmitter 434, shown as TX1 in the figure, and a second transmitter436, shown as TX2 in the figure. Transmitter section 432 is coupled witha receiver (not shown) via an electrical cable 442. The receiver sectionis embodied as an MRC receiver and could be either RX 404 (FIG. 4D) orRX 374 (FIG. 4E). TX1 434 is wired to transmit an analog signal 438 overthe ˜/N wire pair and TX2 is wired to transmit an analog signal 440 overthe N/G wire pair. In digital communication, signals are transmitted bymodulating them over different frequencies, or frequency ranges. Theelectromagnetic wave over which a signal is modulated over is referredto as a carrier wave. In the embodiment of FIG. 4F, two separatedisjoint carrier wave ranges are defined, as shown via an arrow 444 andan arrow 446. A graph 448 shows the power spectral density (hereinabbreviated PSD), in units of Watts per Hertz (herein abbreviated W/Hz),as a function of the frequency, as measured in MHz, of a first set ofcarrier waves. The PSD substantially refers to the power carried by acarrier wave, per unit of frequency. As shown in graph 448, a subset ofthe frequency range shown in the graph has a substantial PSD, shown assteps 450. A graph 452 shows the PSD, in units of W/Hz, as a function ofthe frequency, as measured in MHz of a second set of carrier waves. Asshown in graph 452, another subset of the frequency range shown in thegraph has a substantial PSD, shown as steps 454. The first set ofcarrier waves in graph 448 and the second set of carrier waves in graph452 are disjoint, meaning they represent mutually exclusive groups.

In the embodiment shown in FIG. 4F, a processor (not shown) coupled withtransmitter section 432, determines for each signal to be transferredover electrical cable 442 the frequency of the carrier wave to be used.If the frequency of the carrier wave to be used for a given signal is inthe range of the first set of carrier waves, as shown in graph 448, thenthe processor provides the signal to TX1 434, which transmits the signalover the ˜/N wire pair. If the frequency of the carrier wave to be usedfor a given signal is in the range of the second set of carrier waves,as shown in graph 452, then the processor provides the signal to TX2436, which transmits the signal over the N/G wire pair. In general, theembodiment of FIG. 4F enables different carrier wave frequency ranges tobe defined for each wire pair used to transmit signals. This embodimentcan be used when one wire pair may exhibit better transmissioncharacteristics in a first frequency range and another wire pair mayexhibit better transmission characteristics in a second frequency range.Transmission characteristics can include the noise level on a wire pair.In this respect, transmitter section 432 can transmit signals using twodifferent channels as the term is used in radio and wirelesscommunications, with one channel being the frequency range shown ingraph 448 and another channel being the frequency range shown in graph452. A processor (not shown) determines what the frequency ranges are ofeach channel. As mentioned above, the choice of channel used, i.e.,which carrier wave to transmit a signal on, is determined by theprocessor per signal to be transmitted. For example, a first signal maybe transferred as analog signal 438, a second signal may also betransferred as analog signal 438 and then a third signal may betransferred as analog signal 440.

In general, the choice of which embodiment, as shown above in FIGS.4A-4F, to use for a PLC network depends on many factors, including thetopology of electrical sockets in a residence, the electrical devicesplugged into those electrical sockets, the type of electricaldistribution used in the residence, the physical distance between nodesand the amount of interference, such as RF ingress, in the vicinity ofthe electrical cables of the residence. It is noted that the protocolused for the PLC network, as well as the permitted levels of poweroutput as a function of the frequency of the carrier wave used can alsodetermine which embodiment is to be selected. For example, the G.HNprotocol for PLC networks uses a bandwidth of 100 MHz for transmittingdata over electrical cables, yet the permitted level of power output issignificantly lower in the higher frequency range of the definedbandwidth (e.g., the range of 0-30 MHz may permit a high level of poweroutput whereas the range of 30-100 MHz may permit a low level of poweroutput). Depending on the factors listed above, a particular residencemay achieve better transmission characteristics by using the entirebandwidth, e.g. 0-100 MHz (one transmission channel regarding thebandwidth), as shown above in any of the embodiments of FIGS. 4A-4E.Likewise, another particular residence may achieve better transmissioncharacteristics by using separate portions of the bandwidth, as shownabove in the embodiment of FIG. 4F (two transmission channels regardingthe bandwidth). It is noted that typical PLC communication systems useorthogonal frequency-division multiplexing (herein abbeviated OFDM)modulation for transmitting data over carrier waves over electricalcables. In OFDM modulation, the bandwidth of the system is divided upinto a large number of carriers, or subcarriers. In such aconfiguration, fluctuations in channel attenuation (regarding thebandwidth) as well as additive noise over the frequency range of thebandwidth may be substantially large. Using the disclosed technique,such as the embodiment of FIG. 4F, enables the processor (not shown) towhich transmitter section 432 is coupled with, to determine and selectthe best one of the two channels for transmitting signals for eachindividual subcarrier or for a group of consecutive subcarriers.

As mentioned above, in the switch embodiments of the disclosed technique(as shown in FIGS. 4A, 4B, 4C and 4E) the wire pair chosen by a TX totransmit to an RX, and the wire pair chosen by an RX to receive a signalfrom a TX, is determined on a node-to-node basis. For example, if aswitched PLC network, according to one of the embodiments shown in FIGS.4A, 4B, 4C and 4E, has three nodes, node A, node B and node C, node Amay determine that to transmit data to node B, the N/G wire pair isbetter, and node C may determine that to transmit data to node B, theN/G wire pair is also better. However, node B may determine that toreceive from node A is best on the N/G wire pair, whereas to receivefrom node C, the ˜/N wire pair is better. In the case of the embodimentsshown in FIGS. 4A and 4C, where a switch is located on the side of theRX, the RX of the receiving node requires knowledge of which node istransmitting to it before a signal is received so that it knows on whichwire pair the received signal should be processed and on which wirepair, the received signal should be discarded. Such knowledge can beprovided to the RX by encoding signals transmitted over electricalcables using a time division multiple access (herein abbreviated TDMA)communication method, where a media access control (herein abbreviatedMAC) frame signal, such as a media access plan signal, is transmitted toan RX before the signal including the data is transmitted. The MAC framesignal substantially includes a plan of the information relating to thesignal (which includes data) to be transmitted in the upcoming timeintervals, which includes from which node the signal is going to comefrom. In this respect, the RX of the receiving node will know from whichnode the signal is coming from and can appropriately select the wirepair over which signals received will be provided for furtherprocessing, according to what was decided between the two nodes. In thecase of the embodiment in FIG. 4B, where the RX of the receiving node iswired to a specific wire pair, and in the case of FIGS. 4D, 4E and 4F,where an MRC technique is used and data received on two of the wirepairs is provided for further processing, a TMDA communication methoddoes not need to be used to encode signals transmitted over electricalcables. It should also be noted that MAC schemes exists in which theidentity of the transmitter is not provided in the MAC frame signal. Insuch a case, if a switch is used on the TX side of a node, such as inthe embodiments shown in FIGS. 4A, 4B and 4E, all the nodes on a networkcan jointly decide on which wire pair to transmit. Unlike otherembodiments described above, where the choice of wire pair to transmitand receive is on a node-to-node basis, the decision to transmit over aparticular wire pair in this embodiment is for the TX side of all nodeson the network, i.e., a decision on a network basis.

Reference is now made to FIG. 5, which is a schematic illustration of amodem of the prior art, generally referenced 470. Modem 470 includes acasing 472, a processor 474, an analog to digital converter 476 (hereinabbreviated ADC), a digital to analog converter 478 (herein abbreviatedDAC), a receiver 480, a transmitter 482 and a power cable 484. ADC 476is coupled with receiver 480 and processor 474. DAC 478 is coupled withtransmitter 482 and processor 474. Receiver 480 and transmitter 482 areelectronically coupled with power cable 484. Casing 472 protects andshields processor 474, ADC 476, DAC 478, receiver 480 and transmitter482. Power cable 484 is a standard power cable that includes threewires, a live wire, a neutral wire and a ground wire and enables modem470 to be plugged into an electrical socket (not shown). Modem 470 iscoupled with an electrical device (not shown), such as a computer,printer, television and the like. Modem 470 enables data signals to betransmitted, as shown by an arrow 486B, as well as received, as shown byan arrow 486A, via electrical cables.

When data is received, an analog electrical signal sent via electricalcables (not shown) is received by receiver 480 via power cable 484. Inmodem 470, the data is received on the ˜/N wire pair. The receiverprovides the analog electrical signal to ADC 476, which converts theanalog electrical signal to a digital electrical signal, which is thenprovided to processor 474. Processor 474 then decodes the digitalelectrical signal, modifies the digital electrical signal, passes thedigital electrical signal to the electrical device it is attached to,and the like. When the electrical device to which modem 470 is coupledwith wants to send a signal via PLC, the signal is provided to processor474. Processor 474 may code, modify and/or process the signal, which isthen provided to DAC 478. DAC 478 converts the digital electrical signalto an analog electrical signal and provides it to transmitter 482, whichtransmits the signal over the ˜/N wire pair of power cable 484.

Reference is now made to FIGS. 6A-6F, which represent variousembodiments of the TXs and RXs shown in FIGS. 4A-4F. As will be shownbelow, the switch, on either the TX side or the RX side of a node in anetwork can be embodied at the level of an analog front end (hereinabbreviated AFE) or at the level of a processor. At the level of theAFE, a physical switch is required to be added to state of the art PLCmodems constructed and operative according to the disclosed technique.At the level of the processor, also known as the chip level, no newelements are required to be added to state of the art PLC modems, ratherthe processor in such PLC modems needs to be reprogrammed. This isexplained below.

Reference is now made to FIG. 6A, which is a schematic illustration of areceiver section of a switched PLC modem, generally referenced 500,constructed and operative in accordance with a further embodiment of thedisclosed technique. For purposes of clarity and simplicity, FIG. 6Aonly shows the receiver section of switched PLC modem 500, as is thecase in FIGS. 6B and 6C. Switched PLC modem 500 also includes atransmitter section (not shown). The transmitter section can be one ofthe transmitter sections described below in FIGS. 6D, 6E and 6F or atransmitter section as is known in the prior art. Switched PLC modem 500includes a casing 502, a processor 504, an ADC 506, a receiver 508, aswitch 510 and a power cable 512. ADC 506 is coupled with receiver 508and processor 504. Switch 510 is coupled with receiver 508, processor504 and power cable 512. Casing 502 protects and shields processor 504,ADC 506, receiver 508 and switch 510. Power cable 512 is a standardpower cable that includes three wires, a live wire, a neutral wire and aground wire and enables switched PLC modem 500 to be plugged into anelectrical socket (not shown). Switched PLC Modem 500 is coupled with anelectrical device (not shown), such as a computer, printer, televisionand the like. Since FIG. 6A only shows the receiver section of switchedPLC modem 500, it can only receive data signals, as shown by an arrow514, via electrical cables.

FIG. 6A represents one embodiment of RX 284 (FIG. 4A) and RX 344 (FIG.4C). Switch 510 enables receiver 508 to be coupled to one of the threewire pairs in power cable 512. In this embodiment, processor 504determines, based on verification of the transmission characteristicsand quality of each wire pair, which wire pair receiver 508 should becoupled with in power cable 512 via switch 510. When a signal isreceived on a particular wire pair, receiver 508 provides the signal toADC 506 which converts the analog signal to a digital signal, which isthen provided to processor 504 for processing.

Reference is now made to FIG. 6B, which is a schematic illustration ofanother receiver section of a switched PLC modem, generally referenced530, constructed and operative in accordance with another embodiment ofthe disclosed technique. For purposes of clarity and simplicity, FIG. 6Bonly shows the receiver section of switched PLC modem 530. Switched PLCmodem 530 also includes a transmitter section (not shown). Thetransmitter section can be one of the transmitter sections describedbelow in FIGS. 6D, 6E and 6F, or a transmitter section as is known inthe prior art. Switched PLC modem 530 includes a casing 532, a processor534, an ADC 536, a switch 538, a first receiver 540, a second receiver542 and a power cable 544. ADC 536 is coupled with switch 538 andprocessor 534. Switch 538 is coupled with first receiver 540, secondreceiver 542 and processor 504. First receiver 540 is coupled with awire pair in power cable 544 and second receiver 542 is coupled with adifferent wire pair in power cable 544. For example, first receiver 540may be coupled with the ˜/N wire pair and second receiver 542 may becoupled with the N/G wire pair. Casing 532 protects and shieldsprocessor 534, ADC 536, first receiver 540, second receiver 542 andswitch 538. Power cable 544 is a standard power cable that includesthree wires, a live wire, a neutral wire and a ground wire and enablesswitched PLC modem 530 to be plugged into an electrical socket (notshown). Switched PLC Modem 530 is coupled with an electrical device (notshown), such as a computer, printer, television and the like. Since FIG.6B only shows the receiver section of switched PLC modem 530, it canonly receive data signals, as shown by an arrow 546, via electricalcables.

FIG. 6B represents another embodiment of RX 284 (FIG. 4A) and RX 344(FIG. 4C). Each of first receiver 540 and second receiver 542 receivessignals from a transmitter (not shown) on both the direct communicationchannel as well as the crosstalk communication channel. Whereas bothreceivers receive signals, only the signals from one receiver isprovided to ADC 536 and then to processor 534. If switch 538 is switchedto first receiver 540, then only the signals received by first receiver540 are provided to ADC 536. If switch 538 is switched to secondreceiver 542, then only the signals received by second receiver 542 areprovided to ADC 536. In this embodiment, processor 534 determines, basedon verification of the transmission characteristics and quality of eachwire pair, which receiver switch 538 should be switched to.

Reference is now made to FIG. 6C, which is a schematic illustration of afurther receiver section of a switched PLC modem, generally referenced560, constructed and operative in accordance with a further embodimentof the disclosed technique. For purposes of clarity and simplicity, FIG.6C only shows the receiver section of switched PLC modem 560. SwitchedPLC modem 560 also includes a transmitter section (not shown). Thetransmitter section can be one of the transmitter sections describedbelow in FIGS. 6D, 6E and 6F, or a transmitter section as is known inthe prior art. Switched PLC modem 560 includes a casing 562, a processor564, a first ADC 566, a second ADC 568, a first receiver 570, a secondreceiver 572 and a power cable 574. First ADC 566 is coupled with firstreceiver 570 and processor 564. Second ADC 568 is coupled with secondreceiver 572 and processor 564. First receiver 570 is coupled with awire pair in power cable 574 and second receiver 572 is coupled with adifferent wire pair in power cable 574. For example, first receiver 570may be coupled with the ˜/G wire pair and second receiver 572 may becoupled with the ˜/N wire pair. Casing 562 protects and shieldsprocessor 564, first ADC 566, second ADC 568, first receiver 570 andsecond receiver 572. Power cable 574 is a standard power cable thatincludes three wires, a live wire, a neutral wire and a ground wire andenables switched PLC modem 560 to be plugged into an electrical socket(not shown). Switched PLC Modem 560 is coupled with an electrical device(not shown), such as a computer, printer, television and the like. SinceFIG. 6C only shows the receiver section of switched PLC modem 560, itcan only receive data signals, as shown by an arrow 576, via electricalcables.

FIG. 6C represents another embodiment of RX 284 (FIG. 4A) and RX 344(FIG. 4C) as well as possible embodiments of RX 404 (FIG. 4D) and RX 374(FIG. 4E). Recall that RX 404 and RX 374 refer to MRC receivers. Inswitched PLC modem 560, switching is executed in processor 564. Each offirst receiver 570 and second receiver 572 receives signals from atransmitter (not shown) on both the direct communication channel as wellas the crosstalk communication channel. Receivers receive signals andprovide those signals to respective ADCs, which convert the analogsignals to digital signals. Both respective digital signals are providedto processor 564. Processor 564 decides which of the digital signalsreceived to demodulate, based on verification of the transmissioncharacteristics and quality of the wire pairs that first receiver 570and second receiver 572 are coupled with.

It is noted that in an alternative to FIG. 6C, a switch (not shown) maybe included in switched PLC modem 560, between processor 564 and firstADC 566 and second ADC 568. In such an embodiment, the digital signalsfrom first ADC 566 and second ADC 568 would be provided to the switch,which would be coupled with, and controlled by processor 564. Dependingon the position of the switch, only one digital signal would be providedto processor 564 for processing.

Reference is now made to FIG. 6D, which is a schematic illustration of atransmitter section of a switched PLC modem, generally referenced 590,constructed and operative in accordance with another embodiment of thedisclosed technique. For purposes of clarity and simplicity, FIG. 6Donly shows the transmitter section of switched PLC modem 590, as is thecase in FIGS. 6E and 6F. Switched PLC modem 590 also includes a receiversection (not shown). The receiver section can be one of the receiversections described above in FIGS. 6A, 6B and 6C, or a receiver sectionas is known in the prior art. Switched PLC modem 590 includes a casing592, a processor 594, a DAC 596, a switch 598, a first transmitter 600,a second transmitter 602 and a power cable 604. DAC 596 is coupled withswitch 598 and processor 594. Switch 598 is coupled with firsttransmitter 600, second transmitter 602 and processor 594. Firsttransmitter 600 is coupled with a wire pair in power cable 604 andsecond transmitter 602 is coupled with a different wire pair in powercable 604. For example, first transmitter 600 may be coupled with the˜/G wire pair and second transmitter 602 may be coupled with the N/Gwire pair. Casing 592 protects and shields processor 594, DAC 596, firsttransmitter 600, second transmitter 602 and switch 598. Power cable 604is a standard power cable that includes three wires, a live wire, aneutral wire and a ground wire and enables switched PLC modem 590 to beplugged into an electrical socket (not shown). Switched PLC Modem 590 iscoupled with an electrical device (not shown), such as a computer,printer, television and the like. Since FIG. 6D only shows thetransmitter section of switched PLC modem 590, it can only transmit datasignals, as shown by an arrow 606, via electrical cables.

FIG. 6D represents an embodiment of TX 282 (FIG. 4A), TX 312 (FIG. 4B)and TX 372 (FIG. 4E). Each of first transmitter 600 and secondtransmitter 602 transmits signals to a receiver (not shown) on both thedirect communication channel as well as the crosstalk communicationchannel. Whereas both transmitters can transmit signals, only onetransmitter transmits the signal provided to it by DAC 596, fromprocessor 594. If switch 598 is switched to first transmitter 600, thenDAC 596 only provides signals for transmission to first transmitter 600.If switch 598 is switched to second transmitter 602, then DAC 596 onlyprovides signals for transmission to second transmitter 602. In thisembodiment, processor 594 determines, based on verification of thetransmission characteristics and quality of each wire pair, whichtransmitter switch 598 should be switched to. In another embodiment ofFIG. 6D, the processor (not shown) in the receiver (not shown)determines which wire pair switched PLC modem 590 should transmit over.In this embodiment, the receiver provides a signal to processor 594,instructing it to shift switch 598 to a particular transmitter.

Reference is now made to FIG. 6E, which is a schematic illustration ofanother transmitter section of a switched PLC modem, generallyreferenced 620, constructed and operative in accordance with a furtherembodiment of the disclosed technique. For purposes of clarity andsimplicity, FIG. 6E only shows the transmitter section of switched PLCmodem 620. Switched PLC modem 620 also includes a receiver section (notshown). The receiver section can be one of the receiver sectionsdescribed above in FIGS. 6A, 6B and 6C or a receiver section as is knownin the prior art. Switched PLC modem 620 includes a casing 622, aprocessor 624, a DAC 626, a transmitter 628, a switch 630 and a powercable 632. DAC 626 is coupled with transmitter 628 and processor 624.Switch 630 is coupled with transmitter 628, processor 624 and powercable 632. Casing 622 protects and shields processor 624, DAC 626,transmitter 628 and switch 630. Power cable 632 is a standard powercable that includes three wires, a live wire, a neutral wire and aground wire and enables switched PLC modem 620 to be plugged into anelectrical socket (not shown). Switched PLC Modem 620 is coupled with anelectrical device (not shown), such as a computer, printer, televisionand the like. Since FIG. 6E only shows the transmitter section ofswitched PLC modem 620, it can only transmit data signals, as shown byan arrow 634, via electrical cables.

FIG. 6E represents another embodiment of TX 282 (FIG. 4A), TX 312 (FIG.4B) and TX 372 (FIG. 4E). Switch 630 enables transmitter 628 to becoupled to one of the three wire pairs in power cable 632. In thisembodiment, processor 624 determines, based on verification of thetransmission characteristics and quality of each wire pair, which wirepair transmitter 628 should be coupled with in power cable 632 viaswitch 630. When a signal is to be transmitted, processor 624 providesthe signal to DAC 626 which converts the digital signal to an analogsignal and provides the analog signal to transmitter 628. Depending onwhich wire pair switch 630 is switched to, transmitter 628 will transmitthe analog signal along that wire pair. In another embodiment of FIG.6E, the processor (not shown) in the receiver (not shown) determineswhich wire pair switched PLC modem 620 should transmit over. In thisembodiment, the receiver provides a signal to processor 624, instructingit to shift switch 630 to a particular wire pair.

Reference is now made to FIG. 6F, which is a schematic illustration of afurther transmitter section of a switched PLC modem, generallyreferenced 650, constructed and operative in accordance with anotherembodiment of the disclosed technique. For purposes of clarity andsimplicity, FIG. 6F only shows the transmitter section of switched PLCmodem 650. Switched PLC modem 650 also includes a receiver section (notshown). The receiver section can be one of the receiver sectionsdescribed above in FIGS. 6A, 6B and 6C, or a receiver section as isknown in the prior art. Switched PLC modem 650 includes a casing 652, aprocessor 654, a first DAC 656, a second DAC 658, a first transmitter660, a second transmitter 662 and a power cable 664. First DAC 656 iscoupled with first transmitter 660 and processor 654. Second DAC 658 iscoupled with second transmitter 662 and processor 654. First transmitter660 is coupled with a wire pair in power cable 664 and secondtransmitter 662 is coupled with a different wire pair in power cable664. For example, first transmitter 660 may be coupled with the ˜/N wirepair and second transmitter 662 may be coupled with the ˜/G wire pair.Casing 652 protects and shields processor 654, first DAC 656, second DAC658, first transmitter 660 and second transmitter 662. Power cable 664is a standard power cable that includes three wires, a live wire, aneutral wire and a ground wire and enables switched PLC modem 650 to beplugged into an electrical socket (not shown). Switched PLC Modem 650 iscoupled with an electrical device (not shown), such as a computer,printer, television and the like. Since FIG. 6F only shows thetransmitter section of switched PLC modem 650, it can only transmit datasignals, as shown by an arrow 666, via electrical cables.

FIG. 6F represents another embodiment of TX 282 (FIG. 4A), TX 312 (FIG.4B) and TX 372 (FIG. 4E) as well as a possible embodiment of transmittersection 432 (FIG. 4F). Recall that transmitter section 432 refers to aper carrier PLC configuration with two transmitters. In switched PLCmodem 650, switching is executed in processor 654. Each of firsttransmitter 660 and second transmitter 662 transmits signals to areceiver (not shown) on both the direct communication channel as well asthe crosstalk communication channel. Processor 654 decides which DACsignals are to be provided to for transmission, based on verification ofthe transmission characteristics and quality of the wire pairs thatfirst transmitter 660 and second transmitter 662 are coupled with. It isalso noted, that in an embodiment where FIG. 6F is used to enable a PLCmodem with per carrier capabilities, processor 654 determines percarrier to be transmitted, which transmitter is to be used fortransmitting the subcarrier. Each of first transmitter 660 and secondtransmitter 662 is assigned a particular carrier subset (i.e., frequencyrange) over which it transmits signals. Depending on the carrier usedfor a given signal, processor 654 either provides the signal to DAC 656or DAC 658. For example, if first transmitter 660 transmits carrierwaves in the range of 0-50 MHz and if second transmitter 662 transmitscarrier waves in the range of 50-100 MHz, then if processor 654determines that a particular signal will be transmitter using a carrierwave of 56 MHz, the digital signal will be provided to DAC 658 whichwill convert the digital signal to an analog signal and provide it tosecond transmitter 662. Second transmitter 662 will transmit the signalover the wire pair to which it is coupled with.

It is noted that in an alternative to FIG. 6F, a switch (not shown) maybe included in switched PLC modem 650, between processor 654 and firstDAC 656 and second DAC 658. In such an embodiment, the digital signalsfrom processor 654 would be provided to the switch, which would thenprovide the digital signal to either first DAC 656 or second DAC 658,depending on which wire pair the signal is to be transmitted over ordepending on the frequency of the carrier wave on which the signal is tobe transmitted over. The switch would be controlled by processor 654 andat any given time interval, only one digital signal would be convertedto an analog signal to be transmitted by one of the transmitters.

As mentioned above, it is noted that a PLC modem includes a receiversection and a transmitter section. Accordingly, a PLC modem according tothe disclosed technique can be constructed using any of the embodimentsof the receiver section shown above in FIGS. 6A-6C with any of theembodiments of the transmitter section shown above in FIGS. 6D-6F. Also,a PLC modem according to the disclosed technique can be constructedusing any of the embodiments of the receiver section, as shown in FIGS.6A-6C, with a prior art transmitter section, and a PLC modem accordingto the disclosed technique can further be constructed using any of theembodiments of the transmitter section, as shown in FIGS. 6D-6F, with aprior art receiver section.

In switched PLC networks, TXs and RXs may change the communicationchannel (for example, ˜/N or N/G) over which they respectively transmitand receive signals depending on various factors such as noise level andquality of a given communication channel, either direct or crosstalk.Such factors may be determined at predetermined time intervals. In orderfor a TX or an RX to physically switch the communication channel, the TXor RX may need to temporarily disconnect from the network, or from thetransmission or receiving of signals. If the switching of thecommunication channel is not coordinated between a given TX and RX pairwhich communicate with one another, then signals may not be transmittedor received properly. In addition, signals may not be transmitted andreceived over the communication channel having the lowest level ofnoise, the highest quality or other relevant factors such as thecommunication channel over which an RX receives most of its traffic.According to the disclosed technique, a signal is provided in a preambleframe to a signal transmission frame, such as a data packet, indicatingover which communication channel the upcoming signal transmission framewill be transmitted over. As such, RXs in a network can switch to thedesignated communication channel in a synchronized manner with thetransmission of the upcoming signal transmission frame. Various methodsare provided below in FIGS. 7A-7E for coordinating the selection andchanging of a communication channel between a given TX and RX pair suchthat signals are transmitted and received properly over thecommunication channel. The selection of a given communication channelcan depend on a plurality of factors, such as the communication channelwith the lowest level of noise, the communication channel having thehighest quality, the selection carried out for other TX and RX pairs inthe network linked with the same RX or TX and the like. It is noted thataccording to the disclosed technique, the RX substantially selects thebest communication channel based on a plurality of factors, such as theexample factors listed just above. The criteria for best communicationchannel are a matter of design choice and can vary depending on the sizeof the network, network topology, network traffic and the like. Based onthe methods and schemes described below in FIGS. 7A-7E, it is noted thatother embodiments for coordinating the selection and changing of acommunication channel are possible and obvious to a worker skilled inthe art.

Reference is now made to FIG. 7A, which is a schematic illustration of afirst communication channel coordination scheme in a switched PLCnetwork between two nodes, generally referenced 700, constructed andoperative in accordance with a further embodiment of the disclosedtechnique. In FIG. 7A, signals are transferred between a TX (not shown)and an RX (not shown). First communication channel coordination scheme700 includes two communication channels, an ˜/N communication channel702A and an N/G communication channel 702B. A third communicationchannel (not shown) which would be over the ˜/G wire pair is present infirst communication channel coordination scheme 700 but is not shown forpurposes of clarity. As mentioned above, the selected wire pairs shownin FIGS. 7A-7D are brought merely as an example. In first communicationchannel coordination scheme 700, one of the communication channels ispre-selected as a default communication channel. In FIG. 7A, ˜/Ncommunication channel 702A is pre-selected as the default communicationchannel. Therefore, any node joining the switched PLC network shown inFIG. 7A would first listen to communications on the defaultcommunication channel in an attempt to join the network and determinewhen it can transmit or receive signals over the network.

First communication channel coordination scheme 700 includes a directiveframe 704, a signal transmission frame 706 and a selectiveacknowledgement (herein abbreviated SACK) frame 708. Directive frame 704is a standard frame transmitted before a signal or a signal burst, suchas signal transmission frame 706, is transmitted between the TX and theRX. Directive frame 704 substantially indicates which communicationchannel (or wire pair) the next signal or signal burst will betransmitted over as well as other data such as how long the transmissionwill be. Directive frame 704 may be transmitted over the defaultcommunication channel. Directive frame 704 may also be transmitted overthe other communication channels (or wire pairs) provided that an RXlistening to the default communication channel can receive directiveframe 704 irrespective of which communication channel directive frame704 is transmitted over. In this embodiment, the signal carryingdirective frame 704 should be a robust signal such that the RX canreceive directive frame 704 over any of the communication channels. Forexample, in FIG. 7A, directive frame 704 indicates that signaltransmission frame 706, which is the next signal to be transmitted, willbe transmitted over ˜/N communication channel 702A (i.e., wire pair˜/N). The RX, or network node which may include an RX, on the networkreceiving directive frame 704 then knows which communication channel itshould listen to for receiving the next transmitted signal such assignal transmission frame 706. In addition, if the network node is notsupposed to receive signal transmission frame 706, or if the networknode includes a TX (also not shown) and wants to transmit anothersignal, then directive frame 704 enables the RX in the network node toknow when signal transmission frame 706 is over such that the networknode does not receive signal transmission frame 706 or the network nodewhich includes a TX can now transmit another signal over the networkwithout risk of signal collision. At the end of each signal transmissionframe 706, SACK frame 708 is transmitted. In this embodiment, SACK frame708 is always transmitted over the default communication channel.Therefore, in one embodiment, if directive frame 704 indicated that thesignal transmission frame was to be transmitted over N/G communicationchannel 702B (not shown), then after switching to the N/G wire pair fortransmitting and receiving the signal transmission frame, the TX and theRX would be required to switch back to the default communication channelfor transmitting and receiving SACK frame 708. According to anotherembodiment, the TX and the RX are not required to switch back to thedefault communication channel for transmitting and receiving SACK frame708 provided that the RX can receive SACK frame 708 irrespective ofwhich communication channel it was transmitted over. In this embodiment,the signal carrying SACK frame 708 should be a robust signal such thatit can be received over any of the communication channels. As directiveframe 704 is always transmitted over the default communication channel,the TX and the RX are now both ready to transmit and receive anotherdirective frame (not shown) relating to the next signal transmissionframe (not shown). In such a manner, the switching of communicationchannels between the TX and the RX is coordinated.

The embodiment shown in FIG. 7A enables the use of standard frames intransmitted signals for indicating over which communication channel thenext signal transmission frame will be transmitted over. Such anembodiment involves a relatively simple change to standard MAC framesignals and is also interoperable between standard devices that cancommunication over power lines. It is noted though that directive frame704 may be substantially long, such as on the order of hundreds ofmicroseconds and that directive frame 704 is also proportionallydependent on the time duration of signal transmission frame 706.Therefore, each signal transmission frame transmitted using firstcommunication channel coordination scheme 700 may exhibit a largeoverhead regarding time as each signal transmission frame is required tofirst transmit a directive frame. In addition, any virtual carriersensing (herein abbreviated VCS) indicated in directive frame 704 mayneed to cover an entire signal burst, which can lead to an inefficientusage of signal bursting.

Reference is now made to FIG. 7B, which is a schematic illustration of asecond communication channel coordination scheme in a switched PLCnetwork between two nodes, generally referenced 720, constructed andoperative in accordance with another embodiment of the disclosedtechnique. In FIG. 7B, signals are transferred between a TX (not shown)and an RX (not shown). Second communication channel coordination scheme720 includes two communication channels, an ˜/N communication channel722A and an N/G communication channel 722B. A third communicationchannel (not shown) which would be over the ˜/G wire pair is present insecond communication channel coordination scheme 720 but is not shownfor purposes of clarity. In second communication channel coordinationscheme 720, there is no pre-selected default communication channel as inFIG. 7A.

Second communication channel coordination scheme 720 includes a firstdirective frame 724A, a second directive frame 724B, a first signaltransmission frame 726A, a second signal transmission frame 726B, athird signal transmission frame 726C and a SACK frame 728. First andsecond directive frames 724A and 724B are standard frames similar todirective frame 704 (FIG. 7A) except that first and second directiveframes 724A and 724B substantially indicate that another communicationchannel (or wire pair) is to be used for transmitting and receiving thenext signal or signal burst. For example, in FIG. 7B, first directiveframe 724A indicates that the next, as well as subsequent signaltransmission frames, such as first signal transmission frame 726A andsecond signal transmission frame 726B, will be transmitted over N/Gcommunication channel 722B (i.e., wire pair N/G). As mentioned above,first directive frame 724A could have indicated that the next signaltransmission frame is being transmitted over the ˜/G wire pair. The RXreceiving first directive frame 724A then knows which communicationchannel it should switch to for receiving the next and subsequenttransmitted signals such as first signal transmission frame 726A andsecond signal transmission frame 726B. As such, in second communicationchannel coordination scheme 720, a directive frame is only transmittedwhen the current communication channel is to be switched. The directiveframe then substantially indicates which communication channel is to bethe next current communication channel. In this respect, the directiveframe is always transmitted over the current communication channel. Asshown, SACK frame 728 is transmitted over the current communicationchannel. First directive frame 724A indicated that subsequent signalswould be transmitted over N/G communication channel 722B. As such, N/Gcommunication channel 722B becomes the current communication channel andSACK frame 728 is transmitted over that channel. In this respect, theSACK frame is always transmitted over the current communication channel.In such a manner, the switching of communication channels between the TXand the RX is coordinated.

Second directive frame 724B indicates that the next and subsequentsignals, such as third transmission signal frame 726C and furthertransmission signal frames (not shown), will be transmitted over ˜/Ncommunication channel 722A. Transmission signal frames will then becontinually transmitted over ˜/N communication channel 722A untilotherwise indicated by a subsequent directive frame (not shown).Therefore, according to second communication channel coordination scheme720, a directive frame is only transmitted when the currentcommunication channel (i.e., the wire pair) between the TX and the RXchanges. It is noted that second communication channel coordinationscheme 720, on average, has a reduced overhead regarding time as opposedto first communication channel coordination scheme 700 (FIG. 7A) andsubstantially no overhead regarding time in a switched PLC network whichincludes only two nodes. At the same time it is noted that nodes (i.e.,TXs and RXs) in a switched PLC network using second communicationchannel coordination scheme 720 need to be synchronized and must beaware of what the current communication channel is. For example, nodesin such a network may require some form of memory for knowing what thecurrent communication channel is in the event that a given node losesits synchronization and needs to be resynchronized with the network. Itis also noted that the overhead of the directive frame substantiallydepends on the nature of the signals provided over the network. Iftraffic on the network is high, nodes on the network may switchcommunication channels each signal transmission frame, in which case theoverheard regarding time in second communication channel coordinationscheme 720 would be the same as first communication channel coordinationscheme 700.

Reference is now made to FIG. 7C, which is a schematic illustration of athird communication channel coordination scheme in a switched PLCnetwork between two nodes, generally referenced 740, constructed andoperative in accordance with a further embodiment of the disclosedtechnique. In FIG. 7C, signals are transferred between a TX (not shown)and an RX (not shown). Third communication channel coordination scheme740 includes two communication channels, an ˜/N communication channel742A and an N/G communication channel 742B. A third communicationchannel (not shown) which would be over the ˜/G wire pair is present inthird communication channel coordination scheme 740 but is not shown forpurposes of clarity. In third communication channel coordination scheme740, as in first communication channel coordination scheme 700 (FIG.7A), one of the communication channels is pre-selected as a defaultcommunication channel. In FIG. 7C, ˜/N communication channel 742A ispre-selected as the default communication channel. Therefore, any nodejoining the switched PLC network shown in FIG. 7C would first listen tocommunications on the default communication channel in an attempt tojoin the network and determine when it can transmit or receive signalsover the network.

Third communication channel coordination scheme 740 includes a firstpriority signal 744A, a second priority signal 744B, a contention window746, a synchronization signal 748, an indication signal 750, a signaltransmission frame 752 and a SACK frame 754. First priority signal 744A,second priority signal 744B and contention window 746 are standardsignals transmitted before a signal transmission frame is transmitted.First and second priority signals 744A and 744B are merely brought as anexample. In a given signal transmission frame, a plurality of prioritysignals may be first transmitted indicating the priority of varioussignals to be transmitted by various nodes in the upcoming signaltransmission frame. Contention window 746 is a variable length frame inwhich a draw is conducted amongst all the nodes that want to transmit inthe upcoming signal transmission frame which do not have a specifiedpriority. Contention window 746 substantially eliminates collisions onthe physical line of the network and is known in the art. Aftercontention window 746, synchronization signal 748 is sent to all nodesin the network. Synchronization signal 748 substantially indicates thatthe next signal, indication signal 750, will indicate on whichcommunication channel signal transmission frame 752 will be transmittedover. Indication signal 750 may be embodied as a binary signal such thatits presence indicates that a first communication channel will be usedfor transmitting signal transmission frame 752 and its absence indicatesthat a second communication channel will be used for transmitting signaltransmission frame 752. For example, the presence of indication signal750 may indicate that the next signal will be transmitted over the ˜/Nwire pair, whereas the absence of indication signal 750 may indicatethat the next signal will be transmitted over the N/G wire pair. Sincecontention window 746 is variable in length, synchronization signal 748is required to inform all nodes on the network that the next signal(i.e., indication signal 750) is to be verified as an indicator as towhich communication channel (i.e., wire pair) the upcoming signal (i.e.,signal transmission frame 752) will be transmitted over. In such amanner, the switching of communication channels between the TX and theRX is coordinated.

Synchronization signal 748 and indication signal 750 are non-standardsignals. At the same time, since these signals include less data, thesesignals result in a substantially smaller overheard regarding time ascompared with first communication channel coordination scheme 700 (FIG.7A) and second communication channel coordination scheme 720 (FIG. 7B).It is noted that indication signal 750 can also be embodied as a signalincluding phase information. The phase information is not necessarilybinary and can therefore include an indication of more than two options.Therefore, in this embodiment, indication signal 750 can be used toindicate which of the three possible communication channels (i.e., ˜/G,N/G, ˜/N) the upcoming signal will be transmitted over. After signaltransmission frame 752 is transmitted, SACK frame 754 is transmitted. Asin FIG. 7A, first priority signal 744A, second priority signal 744B,contention window 746, synchronization signal 748, indication signal 750and SACK frame 754 are transmitted over the default communicationchannel, which in FIG. 7C is ˜/N communication channel 742A. Therefore,if indication signal 750 indicates that the next signal transmissionframe is to be transmitted over N/G communication channel 742B, thenaccording to one embodiment after the nodes on the network switched toN/G communication channel 742B, all nodes switch back to the defaultcommunication channel to receive SACK frame 754 and to listen for thenext synchronization signal (not shown) for transmitting and receivingthe next the signal transmission frame (not shown). According to anotherembodiment, the nodes on the network are not required to switch back tothe default communication channel for transmitting and receiving SACKframe 754 provided that the nodes can receive SACK frame 754irrespective of which communication channel it was transmitted over. Inthis embodiment, the signal carrying SACK frame 754 should be a robustsignal such that it can be received over any of the communicationchannels. Synchronization signal 748 and indication signal 750 aretransmitted before each signal transmission frame to indicate to all TXs(not shown) and RXs (not shown) on the network which communicationchannel will be used next for transmitting. In such a manner, theswitching of communication channels between the TXs and the RXs in thenetwork is coordinated.

It is noted that a slight increase in signal collisions may occur inthird communication channel coordination scheme 740 since first andsecond priority signals 744A and 744B may not be seen by all the nodes(not shown) participating in the draw in contention window 746. Inaddition, in the embodiment shown in FIG. 7C, all RXs (or nodes whichare receiving) on the network must switch to another communicationchannel together, if indicated by indication signal 750, as indicationsignal 750 only indicates over which communication channel the upcomingsignal will be transmitted over and not to whom the upcoming signal isdirected to. As synchronization signal 748 and indication signal 750 arenot standard signals, third communication channel coordination scheme740 may require a more complicated change to standard MAC frame signalsas opposed to first and second communication channel coordinationschemes 700 (FIG. 7A) and 720 (FIG. 7B).

Reference is now made to FIG. 7D, which is a schematic illustration of afourth communication channel coordination scheme in a switched PLCnetwork between two nodes, generally referenced 770, constructed andoperative in accordance with another embodiment of the disclosedtechnique. In FIG. 7D, signals are transferred between a TX (not shown)and an RX (not shown). Fourth communication channel coordination scheme770 includes two communication channels, an ˜/N communication channel772A and an N/G communication channel 772B. A third communicationchannel (not shown) which would be over the ˜/G wire pair is present infourth communication channel coordination scheme 770 but is not shownfor purposes of clarity. In fourth communication channel coordinationscheme 770, as in first communication channel coordination scheme 700(FIG. 7A), one of the communication channels is pre-selected as adefault communication channel. In FIG. 7D, ˜/N communication channel772A is pre-selected as the default communication channel. Therefore,any node joining the switched PLC network shown in FIG. 7D would firstlisten to communications on the default communication channel in anattempt to join the network and determine when it can transmit orreceive signals over the network.

Fourth communication channel coordination scheme 770 includes a firstpriority signal 774A, a second priority signal 774B, a contention window776, a signal transmission frame 782 and a SACK frame 784. Contentionwindow 776 is divided up into a first communication channel section 778Aand a second communication channel section 778B, shown by a dotted line780. First and second priority signals 774A and 774B are substantiallysimilar to first and second priority signals 744A and 744B (both fromFIG. 7C). Contention window 776 is substantially similar to contentionwindow 746 (FIG. 7C) except as noted below. As mentioned above, firstand second priority signals 774A and 774B are merely brought as anexample, as in a given signal transmission frame, a plurality ofpriority signals may be first transmitted indicating the priority ofvarious signals to be transmitted by various nodes in the upcomingsignal transmission frame.

Contention window 776 is divided up into first communication channelsection 778A and second communication channel section 778B. Eachcommunication channel section substantially indicates over whichcommunication channel signals in that section will be transmitted over.Therefore, in first communication channel section 778A, a draw may beconducted between all nodes (not shown) wanting to transmit and receiveover ˜/N communication channel 772A and in second communication channelsection 778B, a draw may be conducted between all nodes (not shown)wanting to transmit and receive over N/G communication channel 772B.Based on the various signals in contention window 776, nodes (not shown)in the network know when to switch communication channels based on thelength (i.e., time interval) of first and second communication channelsections 778A and 778B. In such a manner, the switching of communicationchannels between the TX and the RX is coordinated. In this embodiment,during first communication channel section 778A all nodes listen on ˜/Ncommunication channel 772A. Then all nodes switch to N/G communicationchannel 772B and listen to that communication channel during secondcommunication channel section 778B. After signal transmission frame 782,all nodes then switch back to listening to ˜/N communication channel772A to receive SACK frame 784.

As is obvious to one skilled in the art, contention window 776 may bedivided up into a plurality of communication channel sections (notshown) to indicate which of the three wire pairs a given signal will betransmitted over. In addition, as opposed to third communication channelcoordination scheme 740 (FIG. 7C), fourth communication channelcoordination scheme 770 does not include any non-standard signals. Asmentioned above, contention window 776 is a variable length frame inwhich a draw is conducted amongst all the nodes that want to transmit inthe upcoming signal transmission frame which do not have a specifiedpriority. After contention window 776, signal transmission frame 782 istransmitted, followed by SACK frame 784. As in FIG. 7C, first prioritysignal 774A, second priority signal 774B, contention window 776 and SACKframe 784 are transmitted over the default communication channel, whichin FIG. 7D is ˜/N communication channel 772A. In the embodiment shown inFIG. 7D, nodes on the network may continuously be switching between ˜/Ncommunication channel 772A and N/G communication channel 772B as eachcontention window 776 may include signals in each communication channelsection. Furthermore, since SACK frame 784 and contention window 776 arealways transmitted over the default communication channel, according toone embodiment, nodes which transmitted over another communicationchannel must switch back to the default communication channel before thenext signal is transmitted. According to another embodiment, nodes whichtransmitted over another communication channel are not required toswitch back to the default communication channel before the next signalis transmitted provided they can receive SACK frame 784, first prioritysignal 774A, second priority signal 774B and contention window 776irrespective of which communication channel they were transmitted over.In this embodiment, the signals carrying SACK frame 784, first prioritysignal 774A, second priority signal 774B and contention window 776should be robust signals such that they can be received over any of thecommunication channels.

As contention window 776 is variable in length and contention window 776is substantially used to indicate over which communication channel anupcoming transmission will occur, the overhead regarding time in FIG. 7Dmay be substantially smaller than the embodiments shown in FIGS. 7A and7B. At the same time though, the overheard regarding time shown in FIG.7D is scenario dependent and is proportional to the length (i.e., thetime interval) of contention window 776. It is noted that a reduction inthe size of contention window 776 may result in an increase in signalcollisions in the network and as such contention window 776 may need tobe substantially large to enable an efficient use of contention window776 for eliminating or substantially reducing signal collisions in thenetwork. As mentioned above, in this embodiment all RXs in the networkmust switch to the communication channel designated by secondcommunication channel section 778B at the same point in time incontention window 776, as indicated by dotted line 780.

Reference is now made to FIG. 7E, which is a schematic illustration of acommunication channel coordination method in a switched PLC networkbetween a plurality of nodes, constructed and operative in accordancewith a further embodiment of the disclosed technique. The method of FIG.7E represents a fifth communication channel coordination scheme in aswitched PLC network between a plurality of nodes. In a procedure 800,each RX in a switched PLC network examines the TXs it communicates with.For example, some RXs may communicate with only one TX whereas other RXsmay communicate with a plurality of TXs or possibly all TXs in aswitched PLC network. In a procedure 802, based on a plurality offactors, such as the amount of traffic a given RX receives from each TXin the network it communicates with, each RX selects one of the TX's itcommunicates with as a primary TX. In a procedure 804, each RX thendetermines an optimal communication channel between itself and theprimary TX. The determined communication channel can be based on anumber of factors, such as the communication channel with the lowestlevel of noise, the communication channel with the highest quality, andthe like. In this procedure, the factors taken into account to determinethe optimal communication channel relate specifically to the primary TX.In a procedure 806, the given RX then informs all the TXs itcommunicates with of the determined communication channel. The RX thenuses that communication channel to receive signals on permanently, be itfrom the primary TX or any other TX it communicates with. It is notedthat in this procedure, the determined communication channel is thecommunication channel over which the RX receives signals yet notnecessarily the communication channel over which TXs which communicatewith the given RX may transmit signals over. For example, a TX mayswitch communication channels over which it transmits each time ittransmits a new signal whereas the RXs it communicates with will onlyreceive on their respective determined communication channels.

In a procedure 808, the RX tracks the communication of signals over thedetermined communication channel between itself and all the TXs in theswitched PLC network it communicates with. Tracking can involve trackingthe quality of the signals received, the number of collisionsexperienced in receiving signals, as well as other criteria such as thethroughput (i.e. the PHY rate), the error rate, the false alarm rate andthe like. In a procedure 810, based on the tracked communication betweenthe RX and each of the TXs it communicates with, the RX can revise thedetermined optimal communication channel and determine another optimalcommunication channel between itself, the primary TX and all the otherTXs it communicates with in the network. After procedure 810, the methodproceeds back to procedure 806, thereby updating the revised determinedoptimal communication channel to all the TXs, including the primary TX,the RX communicates with in the network. In a procedure 812, based onthe tracked communication between the RX and each of the TXs itcommunicates with, the RX can revise the selected primary TX and selectanother TX which it communicates with as the primary TX. After procedure812, the method proceeds back to procedure 804. Since a new TX wasselected as the primary TX, an optimal communication channel needs to bedetermined between the RX and the new primary TX. As shown in FIG. 7E,procedures 810 and 812 can be executed simultaneously or consecutively,in either order. Therefore, based on the tracking of the communicationchannel, a given RX may change the permanent communication channel itreceives over (procedure 810), the primary TX it communicates with(procedure 812), or both (procedures 810 and 812). It is noted that bothof procedures 810 and 812 are optional procedures. In procedure 812, theselection of a new primary TX is executed dynamically, as an RXaccording to the disclosed technique adapts its communication channelbased on the tracking of the communication channel. In each ofprocedures 810 and 812, the revision may occur at pre-determined timeintervals. For example, an RX may revise its determined optimalcommunication channel and selected primary TX every minute, every fiveminutes, every ten seconds and the like. The revision may also occur atpre-determined events or factors determined by the RX on the physicalline of the network. For example, an RX may revise its determinedoptimal communication channel and selected primary TX if the quality ofsignals received drops below a pre-defined threshold, if the number ofreceived signals in a given time period is less than a pre-defined limitand the like. It is noted that the revision occurring in procedures 810and 812 may occur in an RX via a background process. In the method ofFIG. 7E, the need for switching and coordinating between communicationchannels is eliminated. In addition, such an embodiment can be simplyimplemented in standard MAC frame signals and exhibits substantially nooverhead regarding time in two-node networks and in networks dominatedby one-to-many traffic scenarios. Furthermore, since each RX decides ona particular communication channel with a given TX, the signaltransmission performance between the given TX and RX can be tuned tofavor different signal traffic loads.

It will be appreciated by persons skilled in the art that the disclosedtechnique is not limited to what has been particularly shown anddescribed hereinabove. Rather the scope of the disclosed technique isdefined only by the claims, which follow.

1. System, for transmitting and receiving signals over residentialelectrical cables comprising at least one active wire, one neutral wireand one ground wire, said system comprising: at least two power linemodems, each one of said at least two power line modems coupling arespective electrical device with a respective electrical socket, eachsaid respective electrical socket being coupled with said residentialelectrical cables, each one of said at least two power line modemscomprising: a processor; a plurality of transmitters, coupled with saidprocessor, for transmitting said signals; and at least one receiver,coupled with said processor, for receiving said signals; wherein atleast two of said wires forms at least one receive wire pair, wherein atleast two of said wires forms at least one transmit wire pair, whereineach one of said plurality of transmitters defines a respective carrierwave range over said at least one transmit wire pair, wherein saidprocessor determines a frequency carrier wave for said signals when saidsignals are transmitted, wherein a given one of said plurality oftransmitters transmits said signals if said frequency carrier wave is insaid respective carrier wave range of said given one of said pluralityof transmitters.
 2. The system according to claim 1, wherein each saidrespective carrier wave range is disjoint.
 3. The system according toclaim 1, wherein each said respective carrier wave range over said atleast one transmit wire pair is determined on a node-to-node basis. 4.The system according to claim 1, wherein each said respective carrierwave range over said at least one transmit wire pair is determined on anetwork basis.